Source/core/rendering/RenderBlockFlow.cpp - chromium/blink - Git at Google

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
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  * modification, are permitted provided that the following conditions are
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  * notice, this list of conditions and the following disclaimer.
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  * in the documentation and/or other materials provided with the
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  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 #include "config.h"
 #include "core/rendering/RenderBlockFlow.h"

 #include "core/accessibility/AXObjectCache.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLDialogElement.h"
 #include "core/paint/BlockFlowPainter.h"
 #include "core/rendering/HitTestLocation.h"
 #include "core/rendering/RenderFlowThread.h"
 #include "core/rendering/RenderLayer.h"
 #include "core/rendering/RenderMultiColumnFlowThread.h"
 #include "core/rendering/RenderPagedFlowThread.h"
 #include "core/rendering/RenderText.h"
 #include "core/rendering/RenderView.h"
 #include "core/rendering/TextAutosizer.h"
 #include "core/rendering/line/LineWidth.h"
 #include "core/rendering/svg/SVGTextRunRenderingContext.h"
 #include "platform/text/BidiTextRun.h"

 namespace blink {

 bool RenderBlockFlow::s_canPropagateFloatIntoSibling = false;

 struct SameSizeAsMarginInfo {
     uint16_t bitfields;
     LayoutUnit margins[2];
 };

 COMPILE_ASSERT(sizeof(RenderBlockFlow::MarginValues) == sizeof(LayoutUnit[4]), MarginValues_should_stay_small);

 class MarginInfo {
     // Collapsing flags for whether we can collapse our margins with our children's margins.
     bool m_canCollapseWithChildren : 1;
     bool m_canCollapseMarginBeforeWithChildren : 1;
     bool m_canCollapseMarginAfterWithChildren : 1;
     bool m_canCollapseMarginAfterWithLastChild: 1;

     // Whether or not we are a quirky container, i.e., do we collapse away top and bottom
     // margins in our container. Table cells and the body are the common examples. We
     // also have a custom style property for Safari RSS to deal with TypePad blog articles.
     bool m_quirkContainer : 1;

     // This flag tracks whether we are still looking at child margins that can all collapse together at the beginning of a block.
     // They may or may not collapse with the top margin of the block (|m_canCollapseTopWithChildren| tells us that), but they will
     // always be collapsing with one another. This variable can remain set to true through multiple iterations
     // as long as we keep encountering self-collapsing blocks.
     bool m_atBeforeSideOfBlock : 1;

     // This flag is set when we know we're examining bottom margins and we know we're at the bottom of the block.
     bool m_atAfterSideOfBlock : 1;

     // These variables are used to detect quirky margins that we need to collapse away (in table cells
     // and in the body element).
     bool m_hasMarginBeforeQuirk : 1;
     bool m_hasMarginAfterQuirk : 1;
     bool m_determinedMarginBeforeQuirk : 1;

     bool m_discardMargin : 1;

     // These flags track the previous maximal positive and negative margins.
     LayoutUnit m_positiveMargin;
     LayoutUnit m_negativeMargin;

 public:
     MarginInfo(RenderBlockFlow*, LayoutUnit beforeBorderPadding, LayoutUnit afterBorderPadding);

     void setAtBeforeSideOfBlock(bool b) { m_atBeforeSideOfBlock = b; }
     void setAtAfterSideOfBlock(bool b) { m_atAfterSideOfBlock = b; }
     void clearMargin()
     {
         m_positiveMargin = 0;
         m_negativeMargin = 0;
     }
     void setHasMarginBeforeQuirk(bool b) { m_hasMarginBeforeQuirk = b; }
     void setHasMarginAfterQuirk(bool b) { m_hasMarginAfterQuirk = b; }
     void setDeterminedMarginBeforeQuirk(bool b) { m_determinedMarginBeforeQuirk = b; }
     void setPositiveMargin(LayoutUnit p) { ASSERT(!m_discardMargin); m_positiveMargin = p; }
     void setNegativeMargin(LayoutUnit n) { ASSERT(!m_discardMargin); m_negativeMargin = n; }
     void setPositiveMarginIfLarger(LayoutUnit p)
     {
         ASSERT(!m_discardMargin);
         if (p > m_positiveMargin)
             m_positiveMargin = p;
     }
     void setNegativeMarginIfLarger(LayoutUnit n)
     {
         ASSERT(!m_discardMargin);
         if (n > m_negativeMargin)
             m_negativeMargin = n;
     }

     void setMargin(LayoutUnit p, LayoutUnit n) { ASSERT(!m_discardMargin); m_positiveMargin = p; m_negativeMargin = n; }
     void setCanCollapseMarginAfterWithChildren(bool collapse) { m_canCollapseMarginAfterWithChildren = collapse; }
     void setCanCollapseMarginAfterWithLastChild(bool collapse) { m_canCollapseMarginAfterWithLastChild = collapse; }
     void setDiscardMargin(bool value) { m_discardMargin = value; }

     bool atBeforeSideOfBlock() const { return m_atBeforeSideOfBlock; }
     bool canCollapseWithMarginBefore() const { return m_atBeforeSideOfBlock && m_canCollapseMarginBeforeWithChildren; }
     bool canCollapseWithMarginAfter() const { return m_atAfterSideOfBlock && m_canCollapseMarginAfterWithChildren; }
     bool canCollapseMarginBeforeWithChildren() const { return m_canCollapseMarginBeforeWithChildren; }
     bool canCollapseMarginAfterWithChildren() const { return m_canCollapseMarginAfterWithChildren; }
     bool canCollapseMarginAfterWithLastChild() const { return m_canCollapseMarginAfterWithLastChild; }
     bool quirkContainer() const { return m_quirkContainer; }
     bool determinedMarginBeforeQuirk() const { return m_determinedMarginBeforeQuirk; }
     bool hasMarginBeforeQuirk() const { return m_hasMarginBeforeQuirk; }
     bool hasMarginAfterQuirk() const { return m_hasMarginAfterQuirk; }
     LayoutUnit positiveMargin() const { return m_positiveMargin; }
     LayoutUnit negativeMargin() const { return m_negativeMargin; }
     bool discardMargin() const { return m_discardMargin; }
     LayoutUnit margin() const { return m_positiveMargin - m_negativeMargin; }
 };
 static bool inNormalFlow(RenderBox* child)
 {
     RenderBlock* curr = child->containingBlock();
     RenderView* renderView = child->view();
     while (curr && curr != renderView) {
         if (curr->hasColumns() || curr->isRenderFlowThread())
             return true;
         if (curr->isFloatingOrOutOfFlowPositioned())
             return false;
         curr = curr->containingBlock();
     }
     return true;
 }

 void RenderBlockFlow::RenderBlockFlowRareData::trace(Visitor* visitor)
 {
     visitor->trace(m_multiColumnFlowThread);
 }

 RenderBlockFlow::RenderBlockFlow(ContainerNode* node)
     : RenderBlock(node)
 {
     COMPILE_ASSERT(sizeof(MarginInfo) == sizeof(SameSizeAsMarginInfo), MarginInfo_should_stay_small);
     setChildrenInline(true);
 }

 RenderBlockFlow::~RenderBlockFlow()
 {
 }

 void RenderBlockFlow::trace(Visitor* visitor)
 {
     visitor->trace(m_rareData);
     RenderBlock::trace(visitor);
 }

 RenderBlockFlow* RenderBlockFlow::createAnonymous(Document* document)
 {
     RenderBlockFlow* renderer = new RenderBlockFlow(0);
     renderer->setDocumentForAnonymous(document);
     return renderer;
 }

 RenderObject* RenderBlockFlow::layoutSpecialExcludedChild(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
 {
     RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread();
     if (!flowThread)
         return 0;
     setLogicalTopForChild(flowThread, borderBefore() + paddingBefore());
     flowThread->layoutColumns(relayoutChildren, layoutScope);
     determineLogicalLeftPositionForChild(flowThread);
     return flowThread;
 }

 bool RenderBlockFlow::updateLogicalWidthAndColumnWidth()
 {
     bool relayoutChildren = RenderBlock::updateLogicalWidthAndColumnWidth();
     if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
         if (flowThread->needsNewWidth())
             return true;
     }
     return relayoutChildren;
 }

 void RenderBlockFlow::checkForPaginationLogicalHeightChange(LayoutUnit& pageLogicalHeight, bool& pageLogicalHeightChanged, bool& hasSpecifiedPageLogicalHeight)
 {
     if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
         LogicalExtentComputedValues computedValues;
         computeLogicalHeight(LayoutUnit(), logicalTop(), computedValues);
         LayoutUnit columnHeight = computedValues.m_extent - borderAndPaddingLogicalHeight() - scrollbarLogicalHeight();
         pageLogicalHeightChanged = columnHeight != flowThread->columnHeightAvailable();
         flowThread->setColumnHeightAvailable(std::max<LayoutUnit>(columnHeight, 0));
     } else if (hasColumns()) {
         ColumnInfo* colInfo = columnInfo();

         if (!pageLogicalHeight) {
             LayoutUnit oldLogicalHeight = logicalHeight();
             setLogicalHeight(0);
             // We need to go ahead and set our explicit page height if one exists, so that we can
             // avoid doing two layout passes.
             updateLogicalHeight();
             LayoutUnit columnHeight = contentLogicalHeight();
             if (columnHeight > 0) {
                 pageLogicalHeight = columnHeight;
                 hasSpecifiedPageLogicalHeight = true;
             }
             setLogicalHeight(oldLogicalHeight);
         }
         if (colInfo->columnHeight() != pageLogicalHeight && everHadLayout()) {
             colInfo->setColumnHeight(pageLogicalHeight);
             pageLogicalHeightChanged = true;
         }

         if (!hasSpecifiedPageLogicalHeight && !pageLogicalHeight)
             colInfo->clearForcedBreaks();
     } else if (isRenderFlowThread()) {
         RenderFlowThread* flowThread = toRenderFlowThread(this);

         // FIXME: This is a hack to always make sure we have a page logical height, if said height
         // is known. The page logical height thing in LayoutState is meaningless for flow
         // thread-based pagination (page height isn't necessarily uniform throughout the flow
         // thread), but as long as it is used universally as a means to determine whether page
         // height is known or not, we need this. Page height is unknown when column balancing is
         // enabled and flow thread height is still unknown (i.e. during the first layout pass). When
         // it's unknown, we need to prevent the pagination code from assuming page breaks everywhere
         // and thereby eating every top margin. It should be trivial to clean up and get rid of this
         // hack once the old multicol implementation is gone.
         pageLogicalHeight = flowThread->isPageLogicalHeightKnown() ? LayoutUnit(1) : LayoutUnit(0);

         pageLogicalHeightChanged = flowThread->pageLogicalSizeChanged();
     }
 }

 bool RenderBlockFlow::shouldRelayoutForPagination(LayoutUnit& pageLogicalHeight, LayoutUnit layoutOverflowLogicalBottom) const
 {
     // FIXME: We don't balance properly at all in the presence of forced page breaks. We need to understand what
     // the distance between forced page breaks is so that we can avoid making the minimum column height too tall.
     ColumnInfo* colInfo = columnInfo();
     LayoutUnit columnHeight = pageLogicalHeight;
     const int minColumnCount = colInfo->forcedBreaks() + 1;
     const int desiredColumnCount = colInfo->desiredColumnCount();
     if (minColumnCount >= desiredColumnCount) {
         // The forced page breaks are in control of the balancing. Just set the column height to the
         // maximum page break distance.
         if (!pageLogicalHeight) {
             LayoutUnit distanceBetweenBreaks = std::max<LayoutUnit>(colInfo->maximumDistanceBetweenForcedBreaks(),
                 view()->layoutState()->pageLogicalOffset(*this, borderBefore() + paddingBefore() + layoutOverflowLogicalBottom) - colInfo->forcedBreakOffset());
             columnHeight = std::max(colInfo->minimumColumnHeight(), distanceBetweenBreaks);
         }
     } else if (layoutOverflowLogicalBottom > boundedMultiply(pageLogicalHeight, desiredColumnCount)) {
         // Now that we know the intrinsic height of the columns, we have to rebalance them.
         columnHeight = std::max<LayoutUnit>(colInfo->minimumColumnHeight(), ceilf(layoutOverflowLogicalBottom.toFloat() / desiredColumnCount));
     }

     if (columnHeight && columnHeight != pageLogicalHeight) {
         pageLogicalHeight = columnHeight;
         return true;
     }

     return false;
 }

 void RenderBlockFlow::setColumnCountAndHeight(unsigned count, LayoutUnit pageLogicalHeight)
 {
     ColumnInfo* colInfo = columnInfo();
     if (pageLogicalHeight)
         colInfo->setColumnCountAndHeight(count, pageLogicalHeight);

     if (columnCount(colInfo)) {
         setLogicalHeight(borderBefore() + paddingBefore() + colInfo->columnHeight() + borderAfter() + paddingAfter() + scrollbarLogicalHeight());
         m_overflow.clear();
     }
 }

 void RenderBlockFlow::setBreakAtLineToAvoidWidow(int lineToBreak)
 {
     ASSERT(lineToBreak >= 0);
     ensureRareData();
     ASSERT(!m_rareData->m_didBreakAtLineToAvoidWidow);
     m_rareData->m_lineBreakToAvoidWidow = lineToBreak;
 }

 void RenderBlockFlow::setDidBreakAtLineToAvoidWidow()
 {
     ASSERT(!shouldBreakAtLineToAvoidWidow());

     // This function should be called only after a break was applied to avoid widows
     // so assert |m_rareData| exists.
     ASSERT(m_rareData);

     m_rareData->m_didBreakAtLineToAvoidWidow = true;
 }

 void RenderBlockFlow::clearDidBreakAtLineToAvoidWidow()
 {
     if (!m_rareData)
         return;

     m_rareData->m_didBreakAtLineToAvoidWidow = false;
 }

 void RenderBlockFlow::clearShouldBreakAtLineToAvoidWidow() const
 {
     ASSERT(shouldBreakAtLineToAvoidWidow());
     if (!m_rareData)
         return;

     m_rareData->m_lineBreakToAvoidWidow = -1;
 }

 bool RenderBlockFlow::isSelfCollapsingBlock() const
 {
     m_hasOnlySelfCollapsingChildren = RenderBlock::isSelfCollapsingBlock();
     return m_hasOnlySelfCollapsingChildren;
 }

 void RenderBlockFlow::layoutBlock(bool relayoutChildren)
 {
     ASSERT(needsLayout());
     ASSERT(isInlineBlockOrInlineTable() || !isInline());

     // If we are self-collapsing with self-collapsing descendants this will get set to save us burrowing through our
     // descendants every time in |isSelfCollapsingBlock|. We reset it here so that |isSelfCollapsingBlock| attempts to burrow
     // at least once and so that it always gives a reliable result reflecting the latest layout.
     m_hasOnlySelfCollapsingChildren = false;

     if (!relayoutChildren && simplifiedLayout())
         return;

     SubtreeLayoutScope layoutScope(*this);

     // Multiple passes might be required for column and pagination based layout
     // In the case of the old column code the number of passes will only be two
     // however, in the newer column code the number of passes could equal the
     // number of columns.
     bool done = false;
     LayoutUnit pageLogicalHeight = 0;
     while (!done)
         done = layoutBlockFlow(relayoutChildren, pageLogicalHeight, layoutScope);

     RenderView* renderView = view();
     if (renderView->layoutState()->pageLogicalHeight())
         setPageLogicalOffset(renderView->layoutState()->pageLogicalOffset(*this, logicalTop()));

     updateLayerTransformAfterLayout();

     // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
     // we overflow or not.
     updateScrollInfoAfterLayout();

     if (m_paintInvalidationLogicalTop != m_paintInvalidationLogicalBottom) {
         bool hasVisibleContent = style()->visibility() == VISIBLE;
         if (!hasVisibleContent) {
             RenderLayer* layer = enclosingLayer();
             layer->updateDescendantDependentFlags();
             hasVisibleContent = layer->hasVisibleContent();
         }
         if (hasVisibleContent)
             setShouldInvalidateOverflowForPaint(true);
     }

     if (isHTMLDialogElement(node()) && isOutOfFlowPositioned())
         positionDialog();

     clearNeedsLayout();
 }

 inline bool RenderBlockFlow::layoutBlockFlow(bool relayoutChildren, LayoutUnit &pageLogicalHeight, SubtreeLayoutScope& layoutScope)
 {
     LayoutUnit oldLeft = logicalLeft();
     bool logicalWidthChanged = updateLogicalWidthAndColumnWidth();
     relayoutChildren |= logicalWidthChanged;

     rebuildFloatsFromIntruding();

     bool pageLogicalHeightChanged = false;
     bool hasSpecifiedPageLogicalHeight = false;
     checkForPaginationLogicalHeightChange(pageLogicalHeight, pageLogicalHeightChanged, hasSpecifiedPageLogicalHeight);
     if (pageLogicalHeightChanged)
         relayoutChildren = true;

     LayoutState state(*this, locationOffset(), pageLogicalHeight, pageLogicalHeightChanged, columnInfo(), logicalWidthChanged);

     // We use four values, maxTopPos, maxTopNeg, maxBottomPos, and maxBottomNeg, to track
     // our current maximal positive and negative margins. These values are used when we
     // are collapsed with adjacent blocks, so for example, if you have block A and B
     // collapsing together, then you'd take the maximal positive margin from both A and B
     // and subtract it from the maximal negative margin from both A and B to get the
     // true collapsed margin. This algorithm is recursive, so when we finish layout()
     // our block knows its current maximal positive/negative values.
     //
     // Start out by setting our margin values to our current margins. Table cells have
     // no margins, so we don't fill in the values for table cells.
     if (!isTableCell()) {
         initMaxMarginValues();
         setHasMarginBeforeQuirk(style()->hasMarginBeforeQuirk());
         setHasMarginAfterQuirk(style()->hasMarginAfterQuirk());
         setPaginationStrut(0);
     }

     LayoutUnit beforeEdge = borderBefore() + paddingBefore();
     LayoutUnit afterEdge = borderAfter() + paddingAfter() + scrollbarLogicalHeight();
     LayoutUnit previousHeight = logicalHeight();
     setLogicalHeight(beforeEdge);

     m_paintInvalidationLogicalTop = 0;
     m_paintInvalidationLogicalBottom = 0;
     if (!firstChild() && !isAnonymousBlock())
         setChildrenInline(true);

     TextAutosizer::LayoutScope textAutosizerLayoutScope(this);

     if (childrenInline())
         layoutInlineChildren(relayoutChildren, m_paintInvalidationLogicalTop, m_paintInvalidationLogicalBottom, afterEdge);
     else
         layoutBlockChildren(relayoutChildren, layoutScope, beforeEdge, afterEdge);

     // Expand our intrinsic height to encompass floats.
     if (lowestFloatLogicalBottom() > (logicalHeight() - afterEdge) && createsBlockFormattingContext())
         setLogicalHeight(lowestFloatLogicalBottom() + afterEdge);

     if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
         if (flowThread->recalculateColumnHeights()) {
             setChildNeedsLayout(MarkOnlyThis);
             return false;
         }
     } else if (hasColumns()) {
         OwnPtr<RenderOverflow> savedOverflow = m_overflow.release();
         if (childrenInline())
             addOverflowFromInlineChildren();
         else
             addOverflowFromBlockChildren();
         LayoutUnit layoutOverflowLogicalBottom = (isHorizontalWritingMode() ? layoutOverflowRect().maxY() : layoutOverflowRect().maxX()) - borderBefore() - paddingBefore();
         m_overflow = savedOverflow.release();

         if (!hasSpecifiedPageLogicalHeight && shouldRelayoutForPagination(pageLogicalHeight, layoutOverflowLogicalBottom)) {
             setEverHadLayout(true);
             return false;
         }

         setColumnCountAndHeight(ceilf(layoutOverflowLogicalBottom.toFloat() / pageLogicalHeight.toFloat()), pageLogicalHeight.toFloat());
     }

     if (shouldBreakAtLineToAvoidWidow()) {
         setEverHadLayout(true);
         return false;
     }

     // Calculate our new height.
     LayoutUnit oldHeight = logicalHeight();
     LayoutUnit oldClientAfterEdge = clientLogicalBottom();

     updateLogicalHeight();
     LayoutUnit newHeight = logicalHeight();
     if (oldHeight > newHeight && !childrenInline()) {
         // One of our children's floats may have become an overhanging float for us.
         for (RenderObject* child = lastChild(); child; child = child->previousSibling()) {
             if (child->isRenderBlockFlow() && !child->isFloatingOrOutOfFlowPositioned()) {
                 RenderBlockFlow* block = toRenderBlockFlow(child);
                 if (block->lowestFloatLogicalBottom() + block->logicalTop() <= newHeight)
                     break;
                 addOverhangingFloats(block, false);
             }
         }
     }

     bool heightChanged = (previousHeight != newHeight);
     if (heightChanged)
         relayoutChildren = true;

     layoutPositionedObjects(relayoutChildren || isDocumentElement(), oldLeft != logicalLeft() ? ForcedLayoutAfterContainingBlockMoved : DefaultLayout);

     // Add overflow from children (unless we're multi-column, since in that case all our child overflow is clipped anyway).
     computeOverflow(oldClientAfterEdge);

     m_descendantsWithFloatsMarkedForLayout = false;
     return true;
 }

 void RenderBlockFlow::determineLogicalLeftPositionForChild(RenderBox* child)
 {
     LayoutUnit startPosition = borderStart() + paddingStart();
     LayoutUnit initialStartPosition = startPosition;
     if (style()->shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
         startPosition -= verticalScrollbarWidth();
     LayoutUnit totalAvailableLogicalWidth = borderAndPaddingLogicalWidth() + availableLogicalWidth();

     LayoutUnit childMarginStart = marginStartForChild(child);
     LayoutUnit newPosition = startPosition + childMarginStart;

     LayoutUnit positionToAvoidFloats;
     if (child->avoidsFloats() && containsFloats() && !flowThreadContainingBlock())
         positionToAvoidFloats = startOffsetForLine(logicalTopForChild(child), false, logicalHeightForChild(child));

     // If the child has an offset from the content edge to avoid floats then use that, otherwise let any negative
     // margin pull it back over the content edge or any positive margin push it out.
     // If the child is being centred then the margin calculated to do that has factored in any offset required to
     // avoid floats, so use it if necessary.
     if (style()->textAlign() == WEBKIT_CENTER || child->style()->marginStartUsing(style()).isAuto())
         newPosition = std::max(newPosition, positionToAvoidFloats + childMarginStart);
     else if (positionToAvoidFloats > initialStartPosition)
         newPosition = std::max(newPosition, positionToAvoidFloats);

     setLogicalLeftForChild(child, style()->isLeftToRightDirection() ? newPosition : totalAvailableLogicalWidth - newPosition - logicalWidthForChild(child));
 }

 void RenderBlockFlow::setLogicalLeftForChild(RenderBox* child, LayoutUnit logicalLeft)
 {
     if (isHorizontalWritingMode()) {
         child->setX(logicalLeft);
     } else {
         child->setY(logicalLeft);
     }
 }

 void RenderBlockFlow::setLogicalTopForChild(RenderBox* child, LayoutUnit logicalTop)
 {
     if (isHorizontalWritingMode()) {
         child->setY(logicalTop);
     } else {
         child->setX(logicalTop);
     }
 }

 void RenderBlockFlow::layoutBlockChild(RenderBox* child, MarginInfo& marginInfo, LayoutUnit& previousFloatLogicalBottom)
 {
     LayoutUnit oldPosMarginBefore = maxPositiveMarginBefore();
     LayoutUnit oldNegMarginBefore = maxNegativeMarginBefore();

     // The child is a normal flow object. Compute the margins we will use for collapsing now.
     child->computeAndSetBlockDirectionMargins(this);

     // Try to guess our correct logical top position. In most cases this guess will
     // be correct. Only if we're wrong (when we compute the real logical top position)
     // will we have to potentially relayout.
     LayoutUnit estimateWithoutPagination;
     LayoutUnit logicalTopEstimate = estimateLogicalTopPosition(child, marginInfo, estimateWithoutPagination);

     // Cache our old rect so that we can dirty the proper paint invalidation rects if the child moves.
     LayoutRect oldRect = child->frameRect();
     LayoutUnit oldLogicalTop = logicalTopForChild(child);

     // Go ahead and position the child as though it didn't collapse with the top.
     setLogicalTopForChild(child, logicalTopEstimate);

     RenderBlockFlow* childRenderBlockFlow = child->isRenderBlockFlow() ? toRenderBlockFlow(child) : 0;
     bool markDescendantsWithFloats = false;
     if (logicalTopEstimate != oldLogicalTop && childRenderBlockFlow && !childRenderBlockFlow->avoidsFloats() && childRenderBlockFlow->containsFloats()) {
         markDescendantsWithFloats = true;
     } else if (UNLIKELY(logicalTopEstimate.mightBeSaturated())) {
         // logicalTopEstimate, returned by estimateLogicalTopPosition, might be saturated for
         // very large elements. If it does the comparison with oldLogicalTop might yield a
         // false negative as adding and removing margins, borders etc from a saturated number
         // might yield incorrect results. If this is the case always mark for layout.
         markDescendantsWithFloats = true;
     } else if (!child->avoidsFloats() || child->shrinkToAvoidFloats()) {
         // If an element might be affected by the presence of floats, then always mark it for
         // layout.
         LayoutUnit fb = std::max(previousFloatLogicalBottom, lowestFloatLogicalBottom());
         if (fb > logicalTopEstimate)
             markDescendantsWithFloats = true;
     }

     if (childRenderBlockFlow) {
         if (markDescendantsWithFloats)
             childRenderBlockFlow->markAllDescendantsWithFloatsForLayout();
         if (!child->isWritingModeRoot())
             previousFloatLogicalBottom = std::max(previousFloatLogicalBottom, oldLogicalTop + childRenderBlockFlow->lowestFloatLogicalBottom());
     }

     SubtreeLayoutScope layoutScope(*child);
     if (!child->needsLayout())
         child->markForPaginationRelayoutIfNeeded(layoutScope);

     bool childNeededLayout = child->needsLayout();
     if (childNeededLayout)
         child->layout();

     // Cache if we are at the top of the block right now.
     bool atBeforeSideOfBlock = marginInfo.atBeforeSideOfBlock();
     bool childIsSelfCollapsing = child->isSelfCollapsingBlock();

     // Now determine the correct ypos based off examination of collapsing margin
     // values.
     LayoutUnit logicalTopBeforeClear = collapseMargins(child, marginInfo, childIsSelfCollapsing);

     // Now check for clear.
     LayoutUnit logicalTopAfterClear = clearFloatsIfNeeded(child, marginInfo, oldPosMarginBefore, oldNegMarginBefore, logicalTopBeforeClear, childIsSelfCollapsing);

     bool paginated = view()->layoutState()->isPaginated();
     if (paginated) {
         logicalTopAfterClear = adjustBlockChildForPagination(logicalTopAfterClear, estimateWithoutPagination, child,
             atBeforeSideOfBlock && logicalTopBeforeClear == logicalTopAfterClear);
     }

     setLogicalTopForChild(child, logicalTopAfterClear);

     // Now we have a final top position. See if it really does end up being different from our estimate.
     // clearFloatsIfNeeded can also mark the child as needing a layout even though we didn't move. This happens
     // when collapseMargins dynamically adds overhanging floats because of a child with negative margins.
     if (logicalTopAfterClear != logicalTopEstimate || child->needsLayout() || (paginated && childRenderBlockFlow && childRenderBlockFlow->shouldBreakAtLineToAvoidWidow())) {
         SubtreeLayoutScope layoutScope(*child);
         if (child->shrinkToAvoidFloats()) {
             // The child's width depends on the line width.
             // When the child shifts to clear an item, its width can
             // change (because it has more available line width).
             // So go ahead and mark the item as dirty.
             layoutScope.setChildNeedsLayout(child);
         }

         if (childRenderBlockFlow && !childRenderBlockFlow->avoidsFloats() && childRenderBlockFlow->containsFloats())
             childRenderBlockFlow->markAllDescendantsWithFloatsForLayout();

         if (!child->needsLayout())
             child->markForPaginationRelayoutIfNeeded(layoutScope);

         // Our guess was wrong. Make the child lay itself out again.
         child->layoutIfNeeded();
     }

     // If we previously encountered a self-collapsing sibling of this child that had clearance then
     // we set this bit to ensure we would not collapse the child's margins, and those of any subsequent
     // self-collapsing siblings, with our parent. If this child is not self-collapsing then it can
     // collapse its margins with the parent so reset the bit.
     if (!marginInfo.canCollapseMarginAfterWithLastChild() && !childIsSelfCollapsing)
         marginInfo.setCanCollapseMarginAfterWithLastChild(true);

     // We are no longer at the top of the block if we encounter a non-empty child.
     // This has to be done after checking for clear, so that margins can be reset if a clear occurred.
     if (marginInfo.atBeforeSideOfBlock() && !childIsSelfCollapsing)
         marginInfo.setAtBeforeSideOfBlock(false);

     // Now place the child in the correct left position
     determineLogicalLeftPositionForChild(child);

     LayoutSize childOffset = child->location() - oldRect.location();

     // Update our height now that the child has been placed in the correct position.
     setLogicalHeight(logicalHeight() + logicalHeightForChild(child));
     if (mustSeparateMarginAfterForChild(child)) {
         setLogicalHeight(logicalHeight() + marginAfterForChild(child));
         marginInfo.clearMargin();
     }
     // If the child has overhanging floats that intrude into following siblings (or possibly out
     // of this block), then the parent gets notified of the floats now.
     if (childRenderBlockFlow)
         addOverhangingFloats(childRenderBlockFlow, !childNeededLayout);

     // If the child moved, we have to invalidate its paint as well as any floating/positioned
     // descendants. An exception is if we need a layout. In this case, we know we're going to
     // invalidate our paint (and the child) anyway.
     if (!selfNeedsLayout() && (childOffset.width() || childOffset.height()))
         child->invalidatePaintForOverhangingFloats(true);

     if (paginated) {
         // Check for an after page/column break.
         LayoutUnit newHeight = applyAfterBreak(child, logicalHeight(), marginInfo);
         if (newHeight != height())
             setLogicalHeight(newHeight);
     }
 }

 LayoutUnit RenderBlockFlow::adjustBlockChildForPagination(LayoutUnit logicalTopAfterClear, LayoutUnit estimateWithoutPagination, RenderBox* child, bool atBeforeSideOfBlock)
 {
     RenderBlockFlow* childBlockFlow = child->isRenderBlockFlow() ? toRenderBlockFlow(child) : 0;

     if (estimateWithoutPagination != logicalTopAfterClear) {
         // Our guess prior to pagination movement was wrong. Before we attempt to paginate, let's try again at the new
         // position.
         setLogicalHeight(logicalTopAfterClear);
         setLogicalTopForChild(child, logicalTopAfterClear);

         if (child->shrinkToAvoidFloats()) {
             // The child's width depends on the line width.
             // When the child shifts to clear an item, its width can
             // change (because it has more available line width).
             // So go ahead and mark the item as dirty.
             child->setChildNeedsLayout(MarkOnlyThis);
         }

         SubtreeLayoutScope layoutScope(*child);

         if (childBlockFlow) {
             if (!childBlockFlow->avoidsFloats() && childBlockFlow->containsFloats())
                 childBlockFlow->markAllDescendantsWithFloatsForLayout();
             if (!child->needsLayout())
                 child->markForPaginationRelayoutIfNeeded(layoutScope);
         }

         // Our guess was wrong. Make the child lay itself out again.
         child->layoutIfNeeded();
     }

     LayoutUnit oldTop = logicalTopAfterClear;

     // If the object has a page or column break value of "before", then we should shift to the top of the next page.
     LayoutUnit result = applyBeforeBreak(child, logicalTopAfterClear);

     // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
     LayoutUnit logicalTopBeforeUnsplittableAdjustment = result;
     LayoutUnit logicalTopAfterUnsplittableAdjustment = adjustForUnsplittableChild(child, result);

     LayoutUnit paginationStrut = 0;
     LayoutUnit unsplittableAdjustmentDelta = logicalTopAfterUnsplittableAdjustment - logicalTopBeforeUnsplittableAdjustment;
     LayoutUnit childLogicalHeight = child->logicalHeight();
     if (unsplittableAdjustmentDelta) {
         setPageBreak(result, childLogicalHeight - unsplittableAdjustmentDelta);
         paginationStrut = unsplittableAdjustmentDelta;
     } else if (childBlockFlow && childBlockFlow->paginationStrut()) {
         paginationStrut = childBlockFlow->paginationStrut();
     }

     if (paginationStrut) {
         // We are willing to propagate out to our parent block as long as we were at the top of the block prior
         // to collapsing our margins, and as long as we didn't clear or move as a result of other pagination.
         if (atBeforeSideOfBlock && oldTop == result && !isOutOfFlowPositioned() && !isTableCell()) {
             // FIXME: Should really check if we're exceeding the page height before propagating the strut, but we don't
             // have all the information to do so (the strut only has the remaining amount to push). Gecko gets this wrong too
             // and pushes to the next page anyway, so not too concerned about it.
             setPaginationStrut(result + paginationStrut);
             if (childBlockFlow)
                 childBlockFlow->setPaginationStrut(0);
         } else {
             result += paginationStrut;
         }
     }

     if (!unsplittableAdjustmentDelta) {
         if (LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(result)) {
             LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(result, ExcludePageBoundary);
             LayoutUnit spaceShortage = childLogicalHeight - remainingLogicalHeight;
             if (spaceShortage > 0) {
                 // If the child crosses a column boundary, report a break, in case nothing inside it
                 // has already done so. The column balancer needs to know how much it has to stretch
                 // the columns to make more content fit. If no breaks are reported (but do occur),
                 // the balancer will have no clue. Only measure the space after the last column
                 // boundary, in case it crosses more than one.
                 LayoutUnit spaceShortageInLastColumn = intMod(spaceShortage, pageLogicalHeight);
                 setPageBreak(result, spaceShortageInLastColumn ? spaceShortageInLastColumn : spaceShortage);
             } else if (remainingLogicalHeight == pageLogicalHeight && offsetFromLogicalTopOfFirstPage() + child->logicalTop()) {
                 // We're at the very top of a page or column, and it's not the first one. This child
                 // may turn out to be the smallest piece of content that causes a page break, so we
                 // need to report it.
                 setPageBreak(result, childLogicalHeight);
             }
         }
     }

     // Similar to how we apply clearance. Go ahead and boost height() to be the place where we're going to position the child.
     setLogicalHeight(logicalHeight() + (result - oldTop));

     // Return the final adjusted logical top.
     return result;
 }

 static inline LayoutUnit calculateMinimumPageHeight(RenderStyle* renderStyle, RootInlineBox* lastLine, LayoutUnit lineTop, LayoutUnit lineBottom)
 {
     // We may require a certain minimum number of lines per page in order to satisfy
     // orphans and widows, and that may affect the minimum page height.
     unsigned lineCount = std::max<unsigned>(renderStyle->hasAutoOrphans() ? 1 : renderStyle->orphans(), renderStyle->hasAutoWidows() ? 1 : renderStyle->widows());
     if (lineCount > 1) {
         RootInlineBox* line = lastLine;
         for (unsigned i = 1; i < lineCount && line->prevRootBox(); i++)
             line = line->prevRootBox();

         // FIXME: Paginating using line overflow isn't all fine. See FIXME in
         // adjustLinePositionForPagination() for more details.
         LayoutRect overflow = line->logicalVisualOverflowRect(line->lineTop(), line->lineBottom());
         lineTop = std::min(line->lineTopWithLeading(), overflow.y());
     }
     return lineBottom - lineTop;
 }

 void RenderBlockFlow::adjustLinePositionForPagination(RootInlineBox* lineBox, LayoutUnit& delta, RenderFlowThread* flowThread)
 {
     // FIXME: For now we paginate using line overflow. This ensures that lines don't overlap at all when we
     // put a strut between them for pagination purposes. However, this really isn't the desired rendering, since
     // the line on the top of the next page will appear too far down relative to the same kind of line at the top
     // of the first column.
     //
     // The rendering we would like to see is one where the lineTopWithLeading is at the top of the column, and any line overflow
     // simply spills out above the top of the column. This effect would match what happens at the top of the first column.
     // We can't achieve this rendering, however, until we stop columns from clipping to the column bounds (thus allowing
     // for overflow to occur), and then cache visible overflow for each column rect.
     //
     // Furthermore, the paint we have to do when a column has overflow has to be special. We need to exclude
     // content that paints in a previous column (and content that paints in the following column).
     //
     // For now we'll at least honor the lineTopWithLeading when paginating if it is above the logical top overflow. This will
     // at least make positive leading work in typical cases.
     //
     // FIXME: Another problem with simply moving lines is that the available line width may change (because of floats).
     // Technically if the location we move the line to has a different line width than our old position, then we need to dirty the
     // line and all following lines.
     LayoutRect logicalVisualOverflow = lineBox->logicalVisualOverflowRect(lineBox->lineTop(), lineBox->lineBottom());
     LayoutUnit logicalOffset = std::min(lineBox->lineTopWithLeading(), logicalVisualOverflow.y());
     LayoutUnit logicalBottom = std::max(lineBox->lineBottomWithLeading(), logicalVisualOverflow.maxY());
     LayoutUnit lineHeight = logicalBottom - logicalOffset;
     updateMinimumPageHeight(logicalOffset, calculateMinimumPageHeight(style(), lineBox, logicalOffset, logicalBottom));
     logicalOffset += delta;
     lineBox->setPaginationStrut(0);
     lineBox->setIsFirstAfterPageBreak(false);
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     bool hasUniformPageLogicalHeight = !flowThread || flowThread->regionsHaveUniformLogicalHeight();
     // If lineHeight is greater than pageLogicalHeight, but logicalVisualOverflow.height() still fits, we are
     // still going to add a strut, so that the visible overflow fits on a single page.
     if (!pageLogicalHeight || (hasUniformPageLogicalHeight && logicalVisualOverflow.height() > pageLogicalHeight)) {
         // FIXME: In case the line aligns with the top of the page (or it's slightly shifted downwards) it will not be marked as the first line in the page.
         // From here, the fix is not straightforward because it's not easy to always determine when the current line is the first in the page.
         return;
     }
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);

     int lineIndex = lineCount(lineBox);
     if (remainingLogicalHeight < lineHeight || (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex)) {
         if (shouldBreakAtLineToAvoidWidow() && lineBreakToAvoidWidow() == lineIndex) {
             clearShouldBreakAtLineToAvoidWidow();
             setDidBreakAtLineToAvoidWidow();
         }
         if (lineHeight > pageLogicalHeight) {
             // Split the top margin in order to avoid splitting the visible part of the line.
             remainingLogicalHeight -= std::min(lineHeight - pageLogicalHeight, std::max<LayoutUnit>(0, logicalVisualOverflow.y() - lineBox->lineTopWithLeading()));
         }
         LayoutUnit totalLogicalHeight = lineHeight + std::max<LayoutUnit>(0, logicalOffset);
         LayoutUnit pageLogicalHeightAtNewOffset = hasUniformPageLogicalHeight ? pageLogicalHeight : pageLogicalHeightForOffset(logicalOffset + remainingLogicalHeight);
         setPageBreak(logicalOffset, lineHeight - remainingLogicalHeight);
         if (((lineBox == firstRootBox() && totalLogicalHeight < pageLogicalHeightAtNewOffset) || (!style()->hasAutoOrphans() && style()->orphans() >= lineIndex))
             && !isOutOfFlowPositioned() && !isTableCell()) {
             setPaginationStrut(remainingLogicalHeight + std::max<LayoutUnit>(0, logicalOffset));
         } else {
             delta += remainingLogicalHeight;
             lineBox->setPaginationStrut(remainingLogicalHeight);
             lineBox->setIsFirstAfterPageBreak(true);
         }
     } else if (remainingLogicalHeight == pageLogicalHeight) {
         // We're at the very top of a page or column.
         if (lineBox != firstRootBox())
             lineBox->setIsFirstAfterPageBreak(true);
         if (lineBox != firstRootBox() || offsetFromLogicalTopOfFirstPage())
             setPageBreak(logicalOffset, lineHeight);
     }
 }

 LayoutUnit RenderBlockFlow::adjustForUnsplittableChild(RenderBox* child, LayoutUnit logicalOffset, bool includeMargins)
 {
     bool checkColumnBreaks = view()->layoutState()->isPaginatingColumns() || flowThreadContainingBlock();
     bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight();
     bool isUnsplittable = child->isUnsplittableForPagination() || (checkColumnBreaks && child->style()->columnBreakInside() == PBAVOID)
         || (checkPageBreaks && child->style()->pageBreakInside() == PBAVOID);
     if (!isUnsplittable)
         return logicalOffset;
     LayoutUnit childLogicalHeight = logicalHeightForChild(child) + (includeMargins ? marginBeforeForChild(child) + marginAfterForChild(child) : LayoutUnit());
     LayoutUnit pageLogicalHeight = pageLogicalHeightForOffset(logicalOffset);
     updateMinimumPageHeight(logicalOffset, childLogicalHeight);
     if (!pageLogicalHeight || childLogicalHeight > pageLogicalHeight)
         return logicalOffset;
     LayoutUnit remainingLogicalHeight = pageRemainingLogicalHeightForOffset(logicalOffset, ExcludePageBoundary);
     if (remainingLogicalHeight < childLogicalHeight)
         return logicalOffset + remainingLogicalHeight;
     return logicalOffset;
 }

 void RenderBlockFlow::rebuildFloatsFromIntruding()
 {
     if (m_floatingObjects)
         m_floatingObjects->setHorizontalWritingMode(isHorizontalWritingMode());

     HashSet<RenderBox*> oldIntrudingFloatSet;
     if (!childrenInline() && m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         FloatingObjectSetIterator end = floatingObjectSet.end();
         for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->get();
             if (!floatingObject->isDescendant())
                 oldIntrudingFloatSet.add(floatingObject->renderer());
         }
     }

     // Inline blocks are covered by the isReplaced() check in the avoidFloats method.
     if (avoidsFloats() || isDocumentElement() || isRenderView() || isFloatingOrOutOfFlowPositioned() || isTableCell()) {
         if (m_floatingObjects) {
             m_floatingObjects->clear();
         }
         if (!oldIntrudingFloatSet.isEmpty())
             markAllDescendantsWithFloatsForLayout();
         return;
     }

     RendererToFloatInfoMap floatMap;

     if (m_floatingObjects) {
         if (childrenInline())
             m_floatingObjects->moveAllToFloatInfoMap(floatMap);
         else
             m_floatingObjects->clear();
     }

     // We should not process floats if the parent node is not a RenderBlockFlow. Otherwise, we will add
     // floats in an invalid context. This will cause a crash arising from a bad cast on the parent.
     // See <rdar://problem/8049753>, where float property is applied on a text node in a SVG.
     if (!parent() || !parent()->isRenderBlockFlow())
         return;

     // Attempt to locate a previous sibling with overhanging floats. We skip any elements that
     // may have shifted to avoid floats, and any objects whose floats cannot interact with objects
     // outside it (i.e. objects that create a new block formatting context).
     RenderBlockFlow* parentBlockFlow = toRenderBlockFlow(parent());
     bool parentHasFloats = false;
     RenderObject* prev = previousSibling();
     while (prev && (!prev->isBox() || !prev->isRenderBlock() || toRenderBlock(prev)->avoidsFloats() || toRenderBlock(prev)->createsBlockFormattingContext())) {
         if (prev->isFloating())
             parentHasFloats = true;
         prev = prev->previousSibling();
     }

     // First add in floats from the parent. Self-collapsing blocks let their parent track any floats that intrude into
     // them (as opposed to floats they contain themselves) so check for those here too.
     LayoutUnit logicalTopOffset = logicalTop();
     bool parentHasIntrudingFloats = !parentHasFloats && (!prev || toRenderBlockFlow(prev)->isSelfCollapsingBlock()) && parentBlockFlow->lowestFloatLogicalBottom() > logicalTopOffset;
     if (parentHasFloats || parentHasIntrudingFloats)
         addIntrudingFloats(parentBlockFlow, parentBlockFlow->logicalLeftOffsetForContent(), logicalTopOffset);

     // Add overhanging floats from the previous RenderBlockFlow, but only if it has a float that intrudes into our space.
     if (prev) {
         RenderBlockFlow* blockFlow = toRenderBlockFlow(prev);
         logicalTopOffset -= blockFlow->logicalTop();
         if (blockFlow->lowestFloatLogicalBottom() > logicalTopOffset)
             addIntrudingFloats(blockFlow, 0, logicalTopOffset);
     }

     if (childrenInline()) {
         LayoutUnit changeLogicalTop = LayoutUnit::max();
         LayoutUnit changeLogicalBottom = LayoutUnit::min();
         if (m_floatingObjects) {
             const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
             FloatingObjectSetIterator end = floatingObjectSet.end();
             for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
                 FloatingObject* floatingObject = it->get();
                 FloatingObject* oldFloatingObject = floatMap.get(floatingObject->renderer());
                 LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);
                 if (oldFloatingObject) {
                     LayoutUnit oldLogicalBottom = logicalBottomForFloat(oldFloatingObject);
                     if (logicalWidthForFloat(floatingObject) != logicalWidthForFloat(oldFloatingObject) || logicalLeftForFloat(floatingObject) != logicalLeftForFloat(oldFloatingObject)) {
                         changeLogicalTop = 0;
                         changeLogicalBottom = std::max(changeLogicalBottom, std::max(logicalBottom, oldLogicalBottom));
                     } else {
                         if (logicalBottom != oldLogicalBottom) {
                             changeLogicalTop = std::min(changeLogicalTop, std::min(logicalBottom, oldLogicalBottom));
                             changeLogicalBottom = std::max(changeLogicalBottom, std::max(logicalBottom, oldLogicalBottom));
                         }
                         LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
                         LayoutUnit oldLogicalTop = logicalTopForFloat(oldFloatingObject);
                         if (logicalTop != oldLogicalTop) {
                             changeLogicalTop = std::min(changeLogicalTop, std::min(logicalTop, oldLogicalTop));
                             changeLogicalBottom = std::max(changeLogicalBottom, std::max(logicalTop, oldLogicalTop));
                         }
                     }

                     if (oldFloatingObject->originatingLine() && !selfNeedsLayout()) {
                         ASSERT(oldFloatingObject->originatingLine()->renderer() == this);
                         oldFloatingObject->originatingLine()->markDirty();
                     }

                     floatMap.remove(floatingObject->renderer());
                 } else {
                     changeLogicalTop = 0;
                     changeLogicalBottom = std::max(changeLogicalBottom, logicalBottom);
                 }
             }
         }

         RendererToFloatInfoMap::iterator end = floatMap.end();
         for (RendererToFloatInfoMap::iterator it = floatMap.begin(); it != end; ++it) {
             OwnPtr<FloatingObject>& floatingObject = it->value;
             if (!floatingObject->isDescendant()) {
                 changeLogicalTop = 0;
                 changeLogicalBottom = std::max(changeLogicalBottom, logicalBottomForFloat(floatingObject.get()));
             }
         }

         markLinesDirtyInBlockRange(changeLogicalTop, changeLogicalBottom);
     } else if (!oldIntrudingFloatSet.isEmpty()) {
         // If there are previously intruding floats that no longer intrude, then children with floats
         // should also get layout because they might need their floating object lists cleared.
         if (m_floatingObjects->set().size() < oldIntrudingFloatSet.size()) {
             markAllDescendantsWithFloatsForLayout();
         } else {
             const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
             FloatingObjectSetIterator end = floatingObjectSet.end();
             for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end && !oldIntrudingFloatSet.isEmpty(); ++it)
                 oldIntrudingFloatSet.remove((*it)->renderer());
             if (!oldIntrudingFloatSet.isEmpty())
                 markAllDescendantsWithFloatsForLayout();
         }
     }
 }

 void RenderBlockFlow::layoutBlockChildren(bool relayoutChildren, SubtreeLayoutScope& layoutScope, LayoutUnit beforeEdge, LayoutUnit afterEdge)
 {
     dirtyForLayoutFromPercentageHeightDescendants(layoutScope);

     // The margin struct caches all our current margin collapsing state. The compact struct caches state when we encounter compacts,
     MarginInfo marginInfo(this, beforeEdge, afterEdge);

     // Fieldsets need to find their legend and position it inside the border of the object.
     // The legend then gets skipped during normal layout. The same is true for ruby text.
     // It doesn't get included in the normal layout process but is instead skipped.
     RenderObject* childToExclude = layoutSpecialExcludedChild(relayoutChildren, layoutScope);

     LayoutUnit previousFloatLogicalBottom = 0;

     RenderBox* next = firstChildBox();
     RenderBox* lastNormalFlowChild = 0;

     while (next) {
         RenderBox* child = next;
         next = child->nextSiblingBox();

         child->setMayNeedPaintInvalidation(true);

         if (childToExclude == child)
             continue; // Skip this child, since it will be positioned by the specialized subclass (fieldsets and ruby runs).

         updateBlockChildDirtyBitsBeforeLayout(relayoutChildren, child);

         if (child->isOutOfFlowPositioned()) {
             child->containingBlock()->insertPositionedObject(child);
             adjustPositionedBlock(child, marginInfo);
             continue;
         }
         if (child->isFloating()) {
             insertFloatingObject(child);
             adjustFloatingBlock(marginInfo);
             continue;
         }

         // Lay out the child.
         layoutBlockChild(child, marginInfo, previousFloatLogicalBottom);
         lastNormalFlowChild = child;
     }

     // Now do the handling of the bottom of the block, adding in our bottom border/padding and
     // determining the correct collapsed bottom margin information.
     handleAfterSideOfBlock(lastNormalFlowChild, beforeEdge, afterEdge, marginInfo);
 }

 // Our MarginInfo state used when laying out block children.
 MarginInfo::MarginInfo(RenderBlockFlow* blockFlow, LayoutUnit beforeBorderPadding, LayoutUnit afterBorderPadding)
     : m_canCollapseMarginAfterWithLastChild(true)
     , m_atBeforeSideOfBlock(true)
     , m_atAfterSideOfBlock(false)
     , m_hasMarginBeforeQuirk(false)
     , m_hasMarginAfterQuirk(false)
     , m_determinedMarginBeforeQuirk(false)
     , m_discardMargin(false)
 {
     RenderStyle* blockStyle = blockFlow->style();
     ASSERT(blockFlow->isRenderView() || blockFlow->parent());
     m_canCollapseWithChildren = !blockFlow->createsBlockFormattingContext() && !blockFlow->isRenderFlowThread() && !blockFlow->isRenderView();

     m_canCollapseMarginBeforeWithChildren = m_canCollapseWithChildren && !beforeBorderPadding && blockStyle->marginBeforeCollapse() != MSEPARATE;

     // If any height other than auto is specified in CSS, then we don't collapse our bottom
     // margins with our children's margins. To do otherwise would be to risk odd visual
     // effects when the children overflow out of the parent block and yet still collapse
     // with it. We also don't collapse if we have any bottom border/padding.
     m_canCollapseMarginAfterWithChildren = m_canCollapseWithChildren && !afterBorderPadding
         && (blockStyle->logicalHeight().isAuto() && !blockStyle->logicalHeight().value()) && blockStyle->marginAfterCollapse() != MSEPARATE;

     m_quirkContainer = blockFlow->isTableCell() || blockFlow->isBody();

     m_discardMargin = m_canCollapseMarginBeforeWithChildren && blockFlow->mustDiscardMarginBefore();

     m_positiveMargin = (m_canCollapseMarginBeforeWithChildren && !blockFlow->mustDiscardMarginBefore()) ? blockFlow->maxPositiveMarginBefore() : LayoutUnit();
     m_negativeMargin = (m_canCollapseMarginBeforeWithChildren && !blockFlow->mustDiscardMarginBefore()) ? blockFlow->maxNegativeMarginBefore() : LayoutUnit();
 }

 RenderBlockFlow::MarginValues RenderBlockFlow::marginValuesForChild(RenderBox* child) const
 {
     LayoutUnit childBeforePositive = 0;
     LayoutUnit childBeforeNegative = 0;
     LayoutUnit childAfterPositive = 0;
     LayoutUnit childAfterNegative = 0;

     LayoutUnit beforeMargin = 0;
     LayoutUnit afterMargin = 0;

     RenderBlockFlow* childRenderBlockFlow = child->isRenderBlockFlow() ? toRenderBlockFlow(child) : 0;

     // If the child has the same directionality as we do, then we can just return its
     // margins in the same direction.
     if (!child->isWritingModeRoot()) {
         if (childRenderBlockFlow) {
             childBeforePositive = childRenderBlockFlow->maxPositiveMarginBefore();
             childBeforeNegative = childRenderBlockFlow->maxNegativeMarginBefore();
             childAfterPositive = childRenderBlockFlow->maxPositiveMarginAfter();
             childAfterNegative = childRenderBlockFlow->maxNegativeMarginAfter();
         } else {
             beforeMargin = child->marginBefore();
             afterMargin = child->marginAfter();
         }
     } else if (child->isHorizontalWritingMode() == isHorizontalWritingMode()) {
         // The child has a different directionality. If the child is parallel, then it's just
         // flipped relative to us. We can use the margins for the opposite edges.
         if (childRenderBlockFlow) {
             childBeforePositive = childRenderBlockFlow->maxPositiveMarginAfter();
             childBeforeNegative = childRenderBlockFlow->maxNegativeMarginAfter();
             childAfterPositive = childRenderBlockFlow->maxPositiveMarginBefore();
             childAfterNegative = childRenderBlockFlow->maxNegativeMarginBefore();
         } else {
             beforeMargin = child->marginAfter();
             afterMargin = child->marginBefore();
         }
     } else {
         // The child is perpendicular to us, which means its margins don't collapse but are on the
         // "logical left/right" sides of the child box. We can just return the raw margin in this case.
         beforeMargin = marginBeforeForChild(child);
         afterMargin = marginAfterForChild(child);
     }

     // Resolve uncollapsing margins into their positive/negative buckets.
     if (beforeMargin) {
         if (beforeMargin > 0)
             childBeforePositive = beforeMargin;
         else
             childBeforeNegative = -beforeMargin;
     }
     if (afterMargin) {
         if (afterMargin > 0)
             childAfterPositive = afterMargin;
         else
             childAfterNegative = -afterMargin;
     }

     return RenderBlockFlow::MarginValues(childBeforePositive, childBeforeNegative, childAfterPositive, childAfterNegative);
 }

 LayoutUnit RenderBlockFlow::collapseMargins(RenderBox* child, MarginInfo& marginInfo, bool childIsSelfCollapsing)
 {
     bool childDiscardMarginBefore = mustDiscardMarginBeforeForChild(child);
     bool childDiscardMarginAfter = mustDiscardMarginAfterForChild(child);

     // The child discards the before margin when the the after margin has discard in the case of a self collapsing block.
     childDiscardMarginBefore = childDiscardMarginBefore || (childDiscardMarginAfter && childIsSelfCollapsing);

     // Get the four margin values for the child and cache them.
     const RenderBlockFlow::MarginValues childMargins = marginValuesForChild(child);

     // Get our max pos and neg top margins.
     LayoutUnit posTop = childMargins.positiveMarginBefore();
     LayoutUnit negTop = childMargins.negativeMarginBefore();

     // For self-collapsing blocks, collapse our bottom margins into our
     // top to get new posTop and negTop values.
     if (childIsSelfCollapsing) {
         posTop = std::max(posTop, childMargins.positiveMarginAfter());
         negTop = std::max(negTop, childMargins.negativeMarginAfter());
     }

     // See if the top margin is quirky. We only care if this child has
     // margins that will collapse with us.
     bool topQuirk = hasMarginBeforeQuirk(child);

     if (marginInfo.canCollapseWithMarginBefore()) {
         if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
             // This child is collapsing with the top of the
             // block. If it has larger margin values, then we need to update
             // our own maximal values.
             if (!document().inQuirksMode() || !marginInfo.quirkContainer() || !topQuirk)
                 setMaxMarginBeforeValues(std::max(posTop, maxPositiveMarginBefore()), std::max(negTop, maxNegativeMarginBefore()));

             // The minute any of the margins involved isn't a quirk, don't
             // collapse it away, even if the margin is smaller (www.webreference.com
             // has an example of this, a <dt> with 0.8em author-specified inside
             // a <dl> inside a <td>.
             if (!marginInfo.determinedMarginBeforeQuirk() && !topQuirk && (posTop - negTop)) {
                 setHasMarginBeforeQuirk(false);
                 marginInfo.setDeterminedMarginBeforeQuirk(true);
             }

             if (!marginInfo.determinedMarginBeforeQuirk() && topQuirk && !marginBefore()) {
                 // We have no top margin and our top child has a quirky margin.
                 // We will pick up this quirky margin and pass it through.
                 // This deals with the <td><div><p> case.
                 // Don't do this for a block that split two inlines though. You do
                 // still apply margins in this case.
                 setHasMarginBeforeQuirk(true);
             }
         } else {
             // The before margin of the container will also discard all the margins it is collapsing with.
             setMustDiscardMarginBefore();
         }
     }

     // Once we find a child with discardMarginBefore all the margins collapsing with us must also discard.
     if (childDiscardMarginBefore) {
         marginInfo.setDiscardMargin(true);
         marginInfo.clearMargin();
     }

     if (marginInfo.quirkContainer() && marginInfo.atBeforeSideOfBlock() && (posTop - negTop))
         marginInfo.setHasMarginBeforeQuirk(topQuirk);

     LayoutUnit beforeCollapseLogicalTop = logicalHeight();
     LayoutUnit logicalTop = beforeCollapseLogicalTop;

     LayoutUnit clearanceForSelfCollapsingBlock;
     RenderObject* prev = child->previousSibling();
     RenderBlockFlow* previousBlockFlow =  prev && prev->isRenderBlockFlow() && !prev->isFloatingOrOutOfFlowPositioned() ? toRenderBlockFlow(prev) : 0;
     // If the child's previous sibling is a self-collapsing block that cleared a float then its top border edge has been set at the bottom border edge
     // of the float. Since we want to collapse the child's top margin with the self-collapsing block's top and bottom margins we need to adjust our parent's height to match the
     // margin top of the self-collapsing block. If the resulting collapsed margin leaves the child still intruding into the float then we will want to clear it.
     if (!marginInfo.canCollapseWithMarginBefore() && previousBlockFlow && previousBlockFlow->isSelfCollapsingBlock()) {
         clearanceForSelfCollapsingBlock = previousBlockFlow->marginOffsetForSelfCollapsingBlock();
         setLogicalHeight(logicalHeight() - clearanceForSelfCollapsingBlock);
     }

     if (childIsSelfCollapsing) {
         // For a self collapsing block both the before and after margins get discarded. The block doesn't contribute anything to the height of the block.
         // Also, the child's top position equals the logical height of the container.
         if (!childDiscardMarginBefore && !marginInfo.discardMargin()) {
             // This child has no height. We need to compute our
             // position before we collapse the child's margins together,
             // so that we can get an accurate position for the zero-height block.
             LayoutUnit collapsedBeforePos = std::max(marginInfo.positiveMargin(), childMargins.positiveMarginBefore());
             LayoutUnit collapsedBeforeNeg = std::max(marginInfo.negativeMargin(), childMargins.negativeMarginBefore());
             marginInfo.setMargin(collapsedBeforePos, collapsedBeforeNeg);

             // Now collapse the child's margins together, which means examining our
             // bottom margin values as well.
             marginInfo.setPositiveMarginIfLarger(childMargins.positiveMarginAfter());
             marginInfo.setNegativeMarginIfLarger(childMargins.negativeMarginAfter());

             if (!marginInfo.canCollapseWithMarginBefore()) {
                 // We need to make sure that the position of the self-collapsing block
                 // is correct, since it could have overflowing content
                 // that needs to be positioned correctly (e.g., a block that
                 // had a specified height of 0 but that actually had subcontent).
                 logicalTop = logicalHeight() + collapsedBeforePos - collapsedBeforeNeg;
             }
         }
     } else {
         if (mustSeparateMarginBeforeForChild(child)) {
             ASSERT(!marginInfo.discardMargin() || (marginInfo.discardMargin() && !marginInfo.margin()));
             // If we are at the before side of the block and we collapse, ignore the computed margin
             // and just add the child margin to the container height. This will correctly position
             // the child inside the container.
             LayoutUnit separateMargin = !marginInfo.canCollapseWithMarginBefore() ? marginInfo.margin() : LayoutUnit(0);
             setLogicalHeight(logicalHeight() + separateMargin + marginBeforeForChild(child));
             logicalTop = logicalHeight();
         } else if (!marginInfo.discardMargin() && (!marginInfo.atBeforeSideOfBlock()
             || (!marginInfo.canCollapseMarginBeforeWithChildren()
             && (!document().inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.hasMarginBeforeQuirk())))) {
             // We're collapsing with a previous sibling's margins and not
             // with the top of the block.
             setLogicalHeight(logicalHeight() + std::max(marginInfo.positiveMargin(), posTop) - std::max(marginInfo.negativeMargin(), negTop));
             logicalTop = logicalHeight();
         }

         marginInfo.setDiscardMargin(childDiscardMarginAfter);

         if (!marginInfo.discardMargin()) {
             marginInfo.setPositiveMargin(childMargins.positiveMarginAfter());
             marginInfo.setNegativeMargin(childMargins.negativeMarginAfter());
         } else {
             marginInfo.clearMargin();
         }

         if (marginInfo.margin())
             marginInfo.setHasMarginAfterQuirk(hasMarginAfterQuirk(child));
     }

     // If margins would pull us past the top of the next page, then we need to pull back and pretend like the margins
     // collapsed into the page edge.
     LayoutState* layoutState = view()->layoutState();
     if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTop > beforeCollapseLogicalTop) {
         LayoutUnit oldLogicalTop = logicalTop;
         logicalTop = std::min(logicalTop, nextPageLogicalTop(beforeCollapseLogicalTop));
         setLogicalHeight(logicalHeight() + (logicalTop - oldLogicalTop));
     }

     if (previousBlockFlow) {
         // If |child| is a self-collapsing block it may have collapsed into a previous sibling and although it hasn't reduced the height of the parent yet
         // any floats from the parent will now overhang.
         LayoutUnit oldLogicalHeight = logicalHeight();
         setLogicalHeight(logicalTop);
         if (!previousBlockFlow->avoidsFloats() && (previousBlockFlow->logicalTop() + previousBlockFlow->lowestFloatLogicalBottom()) > logicalTop)
             addOverhangingFloats(previousBlockFlow, false);
         setLogicalHeight(oldLogicalHeight);

         // If |child|'s previous sibling is a self-collapsing block that cleared a float and margin collapsing resulted in |child| moving up
         // into the margin area of the self-collapsing block then the float it clears is now intruding into |child|. Layout again so that we can look for
         // floats in the parent that overhang |child|'s new logical top.
         bool logicalTopIntrudesIntoFloat = clearanceForSelfCollapsingBlock > 0 && logicalTop < beforeCollapseLogicalTop;
         if (logicalTopIntrudesIntoFloat && containsFloats() && !child->avoidsFloats() && lowestFloatLogicalBottom() > logicalTop)
             child->setNeedsLayoutAndFullPaintInvalidation();
     }

     return logicalTop;
 }

 void RenderBlockFlow::adjustPositionedBlock(RenderBox* child, const MarginInfo& marginInfo)
 {
     bool isHorizontal = isHorizontalWritingMode();
     bool hasStaticBlockPosition = child->style()->hasStaticBlockPosition(isHorizontal);

     LayoutUnit logicalTop = logicalHeight();
     updateStaticInlinePositionForChild(child, logicalTop);

     if (!marginInfo.canCollapseWithMarginBefore()) {
         // Positioned blocks don't collapse margins, so add the margin provided by
         // the container now. The child's own margin is added later when calculating its logical top.
         LayoutUnit collapsedBeforePos = marginInfo.positiveMargin();
         LayoutUnit collapsedBeforeNeg = marginInfo.negativeMargin();
         logicalTop += collapsedBeforePos - collapsedBeforeNeg;
     }

     RenderLayer* childLayer = child->layer();
     if (childLayer->staticBlockPosition() != logicalTop) {
         childLayer->setStaticBlockPosition(logicalTop);
         if (hasStaticBlockPosition)
             child->setChildNeedsLayout(MarkOnlyThis);
     }
 }

 LayoutUnit RenderBlockFlow::clearFloatsIfNeeded(RenderBox* child, MarginInfo& marginInfo, LayoutUnit oldTopPosMargin, LayoutUnit oldTopNegMargin, LayoutUnit yPos, bool childIsSelfCollapsing)
 {
     LayoutUnit heightIncrease = getClearDelta(child, yPos);
     if (!heightIncrease)
         return yPos;

     if (childIsSelfCollapsing) {
         bool childDiscardMargin = mustDiscardMarginBeforeForChild(child) || mustDiscardMarginAfterForChild(child);

         // For self-collapsing blocks that clear, they can still collapse their
         // margins with following siblings. Reset the current margins to represent
         // the self-collapsing block's margins only.
         // If DISCARD is specified for -webkit-margin-collapse, reset the margin values.
         RenderBlockFlow::MarginValues childMargins = marginValuesForChild(child);
         if (!childDiscardMargin) {
             marginInfo.setPositiveMargin(std::max(childMargins.positiveMarginBefore(), childMargins.positiveMarginAfter()));
             marginInfo.setNegativeMargin(std::max(childMargins.negativeMarginBefore(), childMargins.negativeMarginAfter()));
         } else {
             marginInfo.clearMargin();
         }
         marginInfo.setDiscardMargin(childDiscardMargin);

         // CSS2.1 states:
         // "If the top and bottom margins of an element with clearance are adjoining, its margins collapse with
         // the adjoining margins of following siblings but that resulting margin does not collapse with the bottom margin of the parent block."
         // So the parent's bottom margin cannot collapse through this block or any subsequent self-collapsing blocks. Set a bit to ensure
         // this happens; it will get reset if we encounter an in-flow sibling that is not self-collapsing.
         marginInfo.setCanCollapseMarginAfterWithLastChild(false);

         // For now set the border-top of |child| flush with the bottom border-edge of the float so it can layout any floating or positioned children of
         // its own at the correct vertical position. If subsequent siblings attempt to collapse with |child|'s margins in |collapseMargins| we will
         // adjust the height of the parent to |child|'s margin top (which if it is positive sits up 'inside' the float it's clearing) so that all three
         // margins can collapse at the correct vertical position.
         // Per CSS2.1 we need to ensure that any negative margin-top clears |child| beyond the bottom border-edge of the float so that the top border edge of the child
         // (i.e. its clearance)  is at a position that satisfies the equation: "the amount of clearance is set so that clearance + margin-top = [height of float],
         // i.e., clearance = [height of float] - margin-top".
         setLogicalHeight(child->logicalTop() + childMargins.negativeMarginBefore());
     } else {
         // Increase our height by the amount we had to clear.
         setLogicalHeight(logicalHeight() + heightIncrease);
     }

     if (marginInfo.canCollapseWithMarginBefore()) {
         // We can no longer collapse with the top of the block since a clear
         // occurred. The empty blocks collapse into the cleared block.
         setMaxMarginBeforeValues(oldTopPosMargin, oldTopNegMargin);
         marginInfo.setAtBeforeSideOfBlock(false);

         // In case the child discarded the before margin of the block we need to reset the mustDiscardMarginBefore flag to the initial value.
         setMustDiscardMarginBefore(style()->marginBeforeCollapse() == MDISCARD);
     }

     return yPos + heightIncrease;
 }

 void RenderBlockFlow::setCollapsedBottomMargin(const MarginInfo& marginInfo)
 {
     if (marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()) {
         // Update the after side margin of the container to discard if the after margin of the last child also discards and we collapse with it.
         // Don't update the max margin values because we won't need them anyway.
         if (marginInfo.discardMargin()) {
             setMustDiscardMarginAfter();
             return;
         }

         // Update our max pos/neg bottom margins, since we collapsed our bottom margins
         // with our children.
         setMaxMarginAfterValues(std::max(maxPositiveMarginAfter(), marginInfo.positiveMargin()), std::max(maxNegativeMarginAfter(), marginInfo.negativeMargin()));

         if (!marginInfo.hasMarginAfterQuirk())
             setHasMarginAfterQuirk(false);

         if (marginInfo.hasMarginAfterQuirk() && !marginAfter()) {
             // We have no bottom margin and our last child has a quirky margin.
             // We will pick up this quirky margin and pass it through.
             // This deals with the <td><div><p> case.
             setHasMarginAfterQuirk(true);
         }
     }
 }

 void RenderBlockFlow::marginBeforeEstimateForChild(RenderBox* child, LayoutUnit& positiveMarginBefore, LayoutUnit& negativeMarginBefore, bool& discardMarginBefore) const
 {
     // Give up if in quirks mode and we're a body/table cell and the top margin of the child box is quirky.
     // Give up if the child specified -webkit-margin-collapse: separate that prevents collapsing.
     // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
     if ((document().inQuirksMode() && hasMarginBeforeQuirk(child) && (isTableCell() || isBody())) || child->style()->marginBeforeCollapse() == MSEPARATE)
         return;

     // The margins are discarded by a child that specified -webkit-margin-collapse: discard.
     // FIXME: Use writing mode independent accessor for marginBeforeCollapse.
     if (child->style()->marginBeforeCollapse() == MDISCARD) {
         positiveMarginBefore = 0;
         negativeMarginBefore = 0;
         discardMarginBefore = true;
         return;
     }

     LayoutUnit beforeChildMargin = marginBeforeForChild(child);
     positiveMarginBefore = std::max(positiveMarginBefore, beforeChildMargin);
     negativeMarginBefore = std::max(negativeMarginBefore, -beforeChildMargin);

     if (!child->isRenderBlockFlow())
         return;

     RenderBlockFlow* childBlockFlow = toRenderBlockFlow(child);
     if (childBlockFlow->childrenInline() || childBlockFlow->isWritingModeRoot())
         return;

     MarginInfo childMarginInfo(childBlockFlow, childBlockFlow->borderBefore() + childBlockFlow->paddingBefore(), childBlockFlow->borderAfter() + childBlockFlow->paddingAfter());
     if (!childMarginInfo.canCollapseMarginBeforeWithChildren())
         return;

     RenderBox* grandchildBox = childBlockFlow->firstChildBox();
     for ( ; grandchildBox; grandchildBox = grandchildBox->nextSiblingBox()) {
         if (!grandchildBox->isFloatingOrOutOfFlowPositioned())
             break;
     }

     // Give up if there is clearance on the box, since it probably won't collapse into us.
     if (!grandchildBox || grandchildBox->style()->clear() != CNONE)
         return;

     // Make sure to update the block margins now for the grandchild box so that we're looking at current values.
     if (grandchildBox->needsLayout()) {
         grandchildBox->computeAndSetBlockDirectionMargins(this);
         if (grandchildBox->isRenderBlock()) {
             RenderBlock* grandchildBlock = toRenderBlock(grandchildBox);
             grandchildBlock->setHasMarginBeforeQuirk(grandchildBox->style()->hasMarginBeforeQuirk());
             grandchildBlock->setHasMarginAfterQuirk(grandchildBox->style()->hasMarginAfterQuirk());
         }
     }

     // Collapse the margin of the grandchild box with our own to produce an estimate.
     childBlockFlow->marginBeforeEstimateForChild(grandchildBox, positiveMarginBefore, negativeMarginBefore, discardMarginBefore);
 }

 LayoutUnit RenderBlockFlow::estimateLogicalTopPosition(RenderBox* child, const MarginInfo& marginInfo, LayoutUnit& estimateWithoutPagination)
 {
     // FIXME: We need to eliminate the estimation of vertical position, because when it's wrong we sometimes trigger a pathological
     // relayout if there are intruding floats.
     LayoutUnit logicalTopEstimate = logicalHeight();
     if (!marginInfo.canCollapseWithMarginBefore()) {
         LayoutUnit positiveMarginBefore = 0;
         LayoutUnit negativeMarginBefore = 0;
         bool discardMarginBefore = false;
         if (child->selfNeedsLayout()) {
             // Try to do a basic estimation of how the collapse is going to go.
             marginBeforeEstimateForChild(child, positiveMarginBefore, negativeMarginBefore, discardMarginBefore);
         } else {
             // Use the cached collapsed margin values from a previous layout. Most of the time they
             // will be right.
             RenderBlockFlow::MarginValues marginValues = marginValuesForChild(child);
             positiveMarginBefore = std::max(positiveMarginBefore, marginValues.positiveMarginBefore());
             negativeMarginBefore = std::max(negativeMarginBefore, marginValues.negativeMarginBefore());
             discardMarginBefore = mustDiscardMarginBeforeForChild(child);
         }

         // Collapse the result with our current margins.
         if (!discardMarginBefore)
             logicalTopEstimate += std::max(marginInfo.positiveMargin(), positiveMarginBefore) - std::max(marginInfo.negativeMargin(), negativeMarginBefore);
     }

     // Adjust logicalTopEstimate down to the next page if the margins are so large that we don't fit on the current
     // page.
     LayoutState* layoutState = view()->layoutState();
     if (layoutState->isPaginated() && layoutState->pageLogicalHeight() && logicalTopEstimate > logicalHeight())
         logicalTopEstimate = std::min(logicalTopEstimate, nextPageLogicalTop(logicalHeight()));

     logicalTopEstimate += getClearDelta(child, logicalTopEstimate);

     estimateWithoutPagination = logicalTopEstimate;

     if (layoutState->isPaginated()) {
         // If the object has a page or column break value of "before", then we should shift to the top of the next page.
         logicalTopEstimate = applyBeforeBreak(child, logicalTopEstimate);

         // For replaced elements and scrolled elements, we want to shift them to the next page if they don't fit on the current one.
         logicalTopEstimate = adjustForUnsplittableChild(child, logicalTopEstimate);

         if (!child->selfNeedsLayout() && child->isRenderBlockFlow())
             logicalTopEstimate += toRenderBlockFlow(child)->paginationStrut();
     }

     return logicalTopEstimate;
 }

 LayoutUnit RenderBlockFlow::marginOffsetForSelfCollapsingBlock()
 {
     ASSERT(isSelfCollapsingBlock());
     RenderBlockFlow* parentBlock = toRenderBlockFlow(parent());
     if (parentBlock && style()->clear() && parentBlock->getClearDelta(this, logicalHeight()))
         return marginValuesForChild(this).positiveMarginBefore();
     return LayoutUnit();
 }

 void RenderBlockFlow::adjustFloatingBlock(const MarginInfo& marginInfo)
 {
     // The float should be positioned taking into account the bottom margin
     // of the previous flow. We add that margin into the height, get the
     // float positioned properly, and then subtract the margin out of the
     // height again. In the case of self-collapsing blocks, we always just
     // use the top margins, since the self-collapsing block collapsed its
     // own bottom margin into its top margin.
     //
     // Note also that the previous flow may collapse its margin into the top of
     // our block. If this is the case, then we do not add the margin in to our
     // height when computing the position of the float. This condition can be tested
     // for by simply calling canCollapseWithMarginBefore. See
     // http://www.hixie.ch/tests/adhoc/css/box/block/margin-collapse/046.html for
     // an example of this scenario.
     LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();
     setLogicalHeight(logicalHeight() + marginOffset);
     positionNewFloats();
     setLogicalHeight(logicalHeight() - marginOffset);
 }

 void RenderBlockFlow::handleAfterSideOfBlock(RenderBox* lastChild, LayoutUnit beforeSide, LayoutUnit afterSide, MarginInfo& marginInfo)
 {
     marginInfo.setAtAfterSideOfBlock(true);

     // If our last child was a self-collapsing block with clearance then our logical height is flush with the
     // bottom edge of the float that the child clears. The correct vertical position for the margin-collapsing we want
     // to perform now is at the child's margin-top - so adjust our height to that position.
     if (lastChild && lastChild->isRenderBlockFlow() && lastChild->isSelfCollapsingBlock())
         setLogicalHeight(logicalHeight() - toRenderBlockFlow(lastChild)->marginOffsetForSelfCollapsingBlock());

     if (marginInfo.canCollapseMarginAfterWithChildren() && !marginInfo.canCollapseMarginAfterWithLastChild())
         marginInfo.setCanCollapseMarginAfterWithChildren(false);

     // If we can't collapse with children then go ahead and add in the bottom margin.
     if (!marginInfo.discardMargin() && (!marginInfo.canCollapseWithMarginAfter() && !marginInfo.canCollapseWithMarginBefore()
         && (!document().inQuirksMode() || !marginInfo.quirkContainer() || !marginInfo.hasMarginAfterQuirk())))
         setLogicalHeight(logicalHeight() + marginInfo.margin());

     // Now add in our bottom border/padding.
     setLogicalHeight(logicalHeight() + afterSide);

     // Negative margins can cause our height to shrink below our minimal height (border/padding).
     // If this happens, ensure that the computed height is increased to the minimal height.
     setLogicalHeight(std::max(logicalHeight(), beforeSide + afterSide));

     // Update our bottom collapsed margin info.
     setCollapsedBottomMargin(marginInfo);
 }

 void RenderBlockFlow::setMustDiscardMarginBefore(bool value)
 {
     if (style()->marginBeforeCollapse() == MDISCARD) {
         ASSERT(value);
         return;
     }

     if (!m_rareData && !value)
         return;

     if (!m_rareData)
         m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));

     m_rareData->m_discardMarginBefore = value;
 }

 void RenderBlockFlow::setMustDiscardMarginAfter(bool value)
 {
     if (style()->marginAfterCollapse() == MDISCARD) {
         ASSERT(value);
         return;
     }

     if (!m_rareData && !value)
         return;

     if (!m_rareData)
         m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));

     m_rareData->m_discardMarginAfter = value;
 }

 bool RenderBlockFlow::mustDiscardMarginBefore() const
 {
     return style()->marginBeforeCollapse() == MDISCARD || (m_rareData && m_rareData->m_discardMarginBefore);
 }

 bool RenderBlockFlow::mustDiscardMarginAfter() const
 {
     return style()->marginAfterCollapse() == MDISCARD || (m_rareData && m_rareData->m_discardMarginAfter);
 }

 bool RenderBlockFlow::mustDiscardMarginBeforeForChild(const RenderBox* child) const
 {
     ASSERT(!child->selfNeedsLayout());
     if (!child->isWritingModeRoot())
         return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginBefore() : (child->style()->marginBeforeCollapse() == MDISCARD);
     if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
         return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginAfter() : (child->style()->marginAfterCollapse() == MDISCARD);

     // FIXME: We return false here because the implementation is not geometrically complete. We have values only for before/after, not start/end.
     // In case the boxes are perpendicular we assume the property is not specified.
     return false;
 }

 bool RenderBlockFlow::mustDiscardMarginAfterForChild(const RenderBox* child) const
 {
     ASSERT(!child->selfNeedsLayout());
     if (!child->isWritingModeRoot())
         return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginAfter() : (child->style()->marginAfterCollapse() == MDISCARD);
     if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
         return child->isRenderBlockFlow() ? toRenderBlockFlow(child)->mustDiscardMarginBefore() : (child->style()->marginBeforeCollapse() == MDISCARD);

     // FIXME: See |mustDiscardMarginBeforeForChild| above.
     return false;
 }

 void RenderBlockFlow::setMaxMarginBeforeValues(LayoutUnit pos, LayoutUnit neg)
 {
     if (!m_rareData) {
         if (pos == RenderBlockFlowRareData::positiveMarginBeforeDefault(this) && neg == RenderBlockFlowRareData::negativeMarginBeforeDefault(this))
             return;
         m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
     }
     m_rareData->m_margins.setPositiveMarginBefore(pos);
     m_rareData->m_margins.setNegativeMarginBefore(neg);
 }

 void RenderBlockFlow::setMaxMarginAfterValues(LayoutUnit pos, LayoutUnit neg)
 {
     if (!m_rareData) {
         if (pos == RenderBlockFlowRareData::positiveMarginAfterDefault(this) && neg == RenderBlockFlowRareData::negativeMarginAfterDefault(this))
             return;
         m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
     }
     m_rareData->m_margins.setPositiveMarginAfter(pos);
     m_rareData->m_margins.setNegativeMarginAfter(neg);
 }

 bool RenderBlockFlow::mustSeparateMarginBeforeForChild(const RenderBox* child) const
 {
     ASSERT(!child->selfNeedsLayout());
     const RenderStyle* childStyle = child->style();
     if (!child->isWritingModeRoot())
         return childStyle->marginBeforeCollapse() == MSEPARATE;
     if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
         return childStyle->marginAfterCollapse() == MSEPARATE;

     // FIXME: See |mustDiscardMarginBeforeForChild| above.
     return false;
 }

 bool RenderBlockFlow::mustSeparateMarginAfterForChild(const RenderBox* child) const
 {
     ASSERT(!child->selfNeedsLayout());
     const RenderStyle* childStyle = child->style();
     if (!child->isWritingModeRoot())
         return childStyle->marginAfterCollapse() == MSEPARATE;
     if (child->isHorizontalWritingMode() == isHorizontalWritingMode())
         return childStyle->marginBeforeCollapse() == MSEPARATE;

     // FIXME: See |mustDiscardMarginBeforeForChild| above.
     return false;
 }

 LayoutUnit RenderBlockFlow::applyBeforeBreak(RenderBox* child, LayoutUnit logicalOffset)
 {
     // FIXME: Add page break checking here when we support printing.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     bool isInsideMulticolFlowThread = flowThread;
     bool checkColumnBreaks = isInsideMulticolFlowThread || view()->layoutState()->isPaginatingColumns();
     bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight(); // FIXME: Once columns can print we have to check this.
     bool checkBeforeAlways = (checkColumnBreaks && child->style()->columnBreakBefore() == PBALWAYS)
         || (checkPageBreaks && child->style()->pageBreakBefore() == PBALWAYS);
     if (checkBeforeAlways && inNormalFlow(child)) {
         if (checkColumnBreaks) {
             if (isInsideMulticolFlowThread) {
                 LayoutUnit offsetBreakAdjustment = 0;
                 if (flowThread->addForcedRegionBreak(offsetFromLogicalTopOfFirstPage() + logicalOffset, child, true, &offsetBreakAdjustment))
                     return logicalOffset + offsetBreakAdjustment;
             } else {
                 view()->layoutState()->addForcedColumnBreak(*child, logicalOffset);
             }
         }
         return nextPageLogicalTop(logicalOffset, IncludePageBoundary);
     }
     return logicalOffset;
 }

 LayoutUnit RenderBlockFlow::applyAfterBreak(RenderBox* child, LayoutUnit logicalOffset, MarginInfo& marginInfo)
 {
     // FIXME: Add page break checking here when we support printing.
     RenderFlowThread* flowThread = flowThreadContainingBlock();
     bool isInsideMulticolFlowThread = flowThread;
     bool checkColumnBreaks = isInsideMulticolFlowThread || view()->layoutState()->isPaginatingColumns();
     bool checkPageBreaks = !checkColumnBreaks && view()->layoutState()->pageLogicalHeight(); // FIXME: Once columns can print we have to check this.
     bool checkAfterAlways = (checkColumnBreaks && child->style()->columnBreakAfter() == PBALWAYS)
         || (checkPageBreaks && child->style()->pageBreakAfter() == PBALWAYS);
     if (checkAfterAlways && inNormalFlow(child)) {
         LayoutUnit marginOffset = marginInfo.canCollapseWithMarginBefore() ? LayoutUnit() : marginInfo.margin();

         // So our margin doesn't participate in the next collapsing steps.
         marginInfo.clearMargin();

         if (checkColumnBreaks) {
             if (isInsideMulticolFlowThread) {
                 LayoutUnit offsetBreakAdjustment = 0;
                 if (flowThread->addForcedRegionBreak(offsetFromLogicalTopOfFirstPage() + logicalOffset + marginOffset, child, false, &offsetBreakAdjustment))
                     return logicalOffset + marginOffset + offsetBreakAdjustment;
             } else {
                 view()->layoutState()->addForcedColumnBreak(*child, logicalOffset);
             }
         }
         return nextPageLogicalTop(logicalOffset, IncludePageBoundary);
     }
     return logicalOffset;
 }

 void RenderBlockFlow::addOverflowFromFloats()
 {
     if (!m_floatingObjects)
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator end = floatingObjectSet.end();
     for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         if (floatingObject->isDescendant())
             addOverflowFromChild(floatingObject->renderer(), IntSize(xPositionForFloatIncludingMargin(floatingObject), yPositionForFloatIncludingMargin(floatingObject)));
     }
 }

 void RenderBlockFlow::computeOverflow(LayoutUnit oldClientAfterEdge, bool recomputeFloats)
 {
     RenderBlock::computeOverflow(oldClientAfterEdge, recomputeFloats);
     if (!hasColumns() && (recomputeFloats || createsBlockFormattingContext() || hasSelfPaintingLayer()))
         addOverflowFromFloats();
 }

 RootInlineBox* RenderBlockFlow::createAndAppendRootInlineBox()
 {
     RootInlineBox* rootBox = createRootInlineBox();
     m_lineBoxes.appendLineBox(rootBox);

     return rootBox;
 }

 void RenderBlockFlow::deleteLineBoxTree()
 {
     if (containsFloats())
         m_floatingObjects->clearLineBoxTreePointers();

     m_lineBoxes.deleteLineBoxTree();
 }

 void RenderBlockFlow::markAllDescendantsWithFloatsForLayout(RenderBox* floatToRemove, bool inLayout)
 {
     if (!everHadLayout() && !containsFloats())
         return;

     if (m_descendantsWithFloatsMarkedForLayout && !floatToRemove)
         return;
     m_descendantsWithFloatsMarkedForLayout |= !floatToRemove;

     MarkingBehavior markParents = inLayout ? MarkOnlyThis : MarkContainingBlockChain;
     setChildNeedsLayout(markParents);

     if (floatToRemove)
         removeFloatingObject(floatToRemove);

     // Iterate over our children and mark them as needed.
     if (!childrenInline()) {
         for (RenderObject* child = firstChild(); child; child = child->nextSibling()) {
             if ((!floatToRemove && child->isFloatingOrOutOfFlowPositioned()) || !child->isRenderBlock())
                 continue;
             if (!child->isRenderBlockFlow()) {
                 RenderBlock* childBlock = toRenderBlock(child);
                 if (childBlock->shrinkToAvoidFloats() && childBlock->everHadLayout())
                     childBlock->setChildNeedsLayout(markParents);
                 continue;
             }
             RenderBlockFlow* childBlockFlow = toRenderBlockFlow(child);
             if ((floatToRemove ? childBlockFlow->containsFloat(floatToRemove) : childBlockFlow->containsFloats()) || childBlockFlow->shrinkToAvoidFloats())
                 childBlockFlow->markAllDescendantsWithFloatsForLayout(floatToRemove, inLayout);
         }
     }
 }

 void RenderBlockFlow::markSiblingsWithFloatsForLayout(RenderBox* floatToRemove)
 {
     if (!m_floatingObjects)
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator end = floatingObjectSet.end();

     for (RenderObject* next = nextSibling(); next; next = next->nextSibling()) {
         if (!next->isRenderBlockFlow() || next->isFloatingOrOutOfFlowPositioned() || toRenderBlockFlow(next)->avoidsFloats())
             continue;

         RenderBlockFlow* nextBlock = toRenderBlockFlow(next);
         for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
             RenderBox* floatingBox = (*it)->renderer();
             if (floatToRemove && floatingBox != floatToRemove)
                 continue;
             if (nextBlock->containsFloat(floatingBox))
                 nextBlock->markAllDescendantsWithFloatsForLayout(floatingBox);
         }
     }
 }

 LayoutUnit RenderBlockFlow::getClearDelta(RenderBox* child, LayoutUnit logicalTop)
 {
     // There is no need to compute clearance if we have no floats.
     if (!containsFloats())
         return 0;

     // At least one float is present. We need to perform the clearance computation.
     bool clearSet = child->style()->clear() != CNONE;
     LayoutUnit logicalBottom = 0;
     switch (child->style()->clear()) {
     case CNONE:
         break;
     case CLEFT:
         logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
         break;
     case CRIGHT:
         logicalBottom = lowestFloatLogicalBottom(FloatingObject::FloatRight);
         break;
     case CBOTH:
         logicalBottom = lowestFloatLogicalBottom();
         break;
     }

     // We also clear floats if we are too big to sit on the same line as a float (and wish to avoid floats by default).
     LayoutUnit result = clearSet ? std::max<LayoutUnit>(0, logicalBottom - logicalTop) : LayoutUnit();
     if (!result && child->avoidsFloats()) {
         LayoutUnit newLogicalTop = logicalTop;
         while (true) {
             LayoutUnit availableLogicalWidthAtNewLogicalTopOffset = availableLogicalWidthForLine(newLogicalTop, false, logicalHeightForChild(child));
             if (availableLogicalWidthAtNewLogicalTopOffset == availableLogicalWidthForContent())
                 return newLogicalTop - logicalTop;

             LayoutRect borderBox = child->borderBoxRect();
             LayoutUnit childLogicalWidthAtOldLogicalTopOffset = isHorizontalWritingMode() ? borderBox.width() : borderBox.height();

             // FIXME: None of this is right for perpendicular writing-mode children.
             LayoutUnit childOldLogicalWidth = child->logicalWidth();
             LayoutUnit childOldMarginLeft = child->marginLeft();
             LayoutUnit childOldMarginRight = child->marginRight();
             LayoutUnit childOldLogicalTop = child->logicalTop();

             child->setLogicalTop(newLogicalTop);
             child->updateLogicalWidth();
             borderBox = child->borderBoxRect();
             LayoutUnit childLogicalWidthAtNewLogicalTopOffset = isHorizontalWritingMode() ? borderBox.width() : borderBox.height();

             child->setLogicalTop(childOldLogicalTop);
             child->setLogicalWidth(childOldLogicalWidth);
             child->setMarginLeft(childOldMarginLeft);
             child->setMarginRight(childOldMarginRight);

             if (childLogicalWidthAtNewLogicalTopOffset <= availableLogicalWidthAtNewLogicalTopOffset) {
                 // Even though we may not be moving, if the logical width did shrink because of the presence of new floats, then
                 // we need to force a relayout as though we shifted. This happens because of the dynamic addition of overhanging floats
                 // from previous siblings when negative margins exist on a child (see the addOverhangingFloats call at the end of collapseMargins).
                 if (childLogicalWidthAtOldLogicalTopOffset != childLogicalWidthAtNewLogicalTopOffset)
                     child->setChildNeedsLayout(MarkOnlyThis);
                 return newLogicalTop - logicalTop;
             }

             newLogicalTop = nextFloatLogicalBottomBelow(newLogicalTop);
             ASSERT(newLogicalTop >= logicalTop);
             if (newLogicalTop < logicalTop)
                 break;
         }
         ASSERT_NOT_REACHED();
     }
     return result;
 }

 void RenderBlockFlow::createFloatingObjects()
 {
     m_floatingObjects = adoptPtr(new FloatingObjects(this, isHorizontalWritingMode()));
 }

 void RenderBlockFlow::styleWillChange(StyleDifference diff, const RenderStyle& newStyle)
 {
     RenderStyle* oldStyle = style();
     s_canPropagateFloatIntoSibling = oldStyle ? !isFloatingOrOutOfFlowPositioned() && !avoidsFloats() : false;
     if (oldStyle && parent() && diff.needsFullLayout() && oldStyle->position() != newStyle.position()
         && containsFloats() && !isFloating() && !isOutOfFlowPositioned() && newStyle.hasOutOfFlowPosition())
             markAllDescendantsWithFloatsForLayout();

     RenderBlock::styleWillChange(diff, newStyle);
 }

 void RenderBlockFlow::styleDidChange(StyleDifference diff, const RenderStyle* oldStyle)
 {
     RenderBlock::styleDidChange(diff, oldStyle);

     // After our style changed, if we lose our ability to propagate floats into next sibling
     // blocks, then we need to find the top most parent containing that overhanging float and
     // then mark its descendants with floats for layout and clear all floats from its next
     // sibling blocks that exist in our floating objects list. See bug 56299 and 62875.
     bool canPropagateFloatIntoSibling = !isFloatingOrOutOfFlowPositioned() && !avoidsFloats();
     if (diff.needsFullLayout() && s_canPropagateFloatIntoSibling && !canPropagateFloatIntoSibling && hasOverhangingFloats()) {
         RenderBlockFlow* parentBlockFlow = this;
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         FloatingObjectSetIterator end = floatingObjectSet.end();

         for (RenderObject* curr = parent(); curr && !curr->isRenderView(); curr = curr->parent()) {
             if (curr->isRenderBlockFlow()) {
                 RenderBlockFlow* currBlock = toRenderBlockFlow(curr);

                 if (currBlock->hasOverhangingFloats()) {
                     for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
                         RenderBox* renderer = (*it)->renderer();
                         if (currBlock->hasOverhangingFloat(renderer)) {
                             parentBlockFlow = currBlock;
                             break;
                         }
                     }
                 }
             }
         }

         parentBlockFlow->markAllDescendantsWithFloatsForLayout();
         parentBlockFlow->markSiblingsWithFloatsForLayout();
     }

     if (diff.needsFullLayout() || !oldStyle)
         createOrDestroyMultiColumnFlowThreadIfNeeded(oldStyle);
 }

 void RenderBlockFlow::updateStaticInlinePositionForChild(RenderBox* child, LayoutUnit logicalTop)
 {
     if (child->style()->isOriginalDisplayInlineType())
         setStaticInlinePositionForChild(child, startAlignedOffsetForLine(logicalTop, false));
     else
         setStaticInlinePositionForChild(child, startOffsetForContent());
 }

 void RenderBlockFlow::setStaticInlinePositionForChild(RenderBox* child, LayoutUnit inlinePosition)
 {
     child->layer()->setStaticInlinePosition(inlinePosition);
 }

 void RenderBlockFlow::addChild(RenderObject* newChild, RenderObject* beforeChild)
 {
     if (RenderMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
         if (beforeChild == flowThread)
             beforeChild = flowThread->firstChild();
         ASSERT(!beforeChild || beforeChild->isDescendantOf(flowThread));
         flowThread->addChild(newChild, beforeChild);
         return;
     }
     RenderBlock::addChild(newChild, beforeChild);
 }

 void RenderBlockFlow::moveAllChildrenIncludingFloatsTo(RenderBlock* toBlock, bool fullRemoveInsert)
 {
     RenderBlockFlow* toBlockFlow = toRenderBlockFlow(toBlock);
     moveAllChildrenTo(toBlockFlow, fullRemoveInsert);

     // When a portion of the render tree is being detached, anonymous blocks
     // will be combined as their children are deleted. In this process, the
     // anonymous block later in the tree is merged into the one preceeding it.
     // It can happen that the later block (this) contains floats that the
     // previous block (toBlockFlow) did not contain, and thus are not in the
     // floating objects list for toBlockFlow. This can result in toBlockFlow containing
     // floats that are not in it's floating objects list, but are in the
     // floating objects lists of siblings and parents. This can cause problems
     // when the float itself is deleted, since the deletion code assumes that
     // if a float is not in it's containing block's floating objects list, it
     // isn't in any floating objects list. In order to preserve this condition
     // (removing it has serious performance implications), we need to copy the
     // floating objects from the old block (this) to the new block (toBlockFlow).
     // The float's metrics will likely all be wrong, but since toBlockFlow is
     // already marked for layout, this will get fixed before anything gets
     // displayed.
     // See bug https://code.google.com/p/chromium/issues/detail?id=230907
     if (m_floatingObjects) {
         if (!toBlockFlow->m_floatingObjects)
             toBlockFlow->createFloatingObjects();

         const FloatingObjectSet& fromFloatingObjectSet = m_floatingObjects->set();
         FloatingObjectSetIterator end = fromFloatingObjectSet.end();

         for (FloatingObjectSetIterator it = fromFloatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->get();

             // Don't insert the object again if it's already in the list
             if (toBlockFlow->containsFloat(floatingObject->renderer()))
                 continue;

             toBlockFlow->m_floatingObjects->add(floatingObject->unsafeClone());
         }
     }

 }

 void RenderBlockFlow::invalidatePaintForOverhangingFloats(bool paintAllDescendants)
 {
     // Invalidate paint of any overhanging floats (if we know we're the one to paint them).
     // Otherwise, bail out.
     if (!hasOverhangingFloats())
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator end = floatingObjectSet.end();
     for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         // Only issue paint invaldiations for the object if it is overhanging, is not in its own layer, and
         // is our responsibility to paint (m_shouldPaint is set). When paintAllDescendants is true, the latter
         // condition is replaced with being a descendant of us.
         if (logicalBottomForFloat(floatingObject) > logicalHeight()
             && !floatingObject->renderer()->hasSelfPaintingLayer()
             && (floatingObject->shouldPaint() || (paintAllDescendants && floatingObject->renderer()->isDescendantOf(this)))) {

             RenderBox* floatingRenderer = floatingObject->renderer();
             floatingRenderer->setShouldDoFullPaintInvalidation();
             floatingRenderer->invalidatePaintForOverhangingFloats(false);
         }
     }
 }

 void RenderBlockFlow::invalidatePaintForOverflow()
 {
     // FIXME: We could tighten up the left and right invalidation points if we let layoutInlineChildren fill them in based off the particular lines
     // it had to lay out. We wouldn't need the hasOverflowClip() hack in that case either.
     LayoutUnit paintInvalidationLogicalLeft = logicalLeftVisualOverflow();
     LayoutUnit paintInvalidationLogicalRight = logicalRightVisualOverflow();
     if (hasOverflowClip()) {
         // If we have clipped overflow, we should use layout overflow as well, since visual overflow from lines didn't propagate to our block's overflow.
         // Note the old code did this as well but even for overflow:visible. The addition of hasOverflowClip() at least tightens up the hack a bit.
         // layoutInlineChildren should be patched to compute the entire paint invalidation rect.
         paintInvalidationLogicalLeft = std::min(paintInvalidationLogicalLeft, logicalLeftLayoutOverflow());
         paintInvalidationLogicalRight = std::max(paintInvalidationLogicalRight, logicalRightLayoutOverflow());
     }

     LayoutRect paintInvalidationRect;
     if (isHorizontalWritingMode())
         paintInvalidationRect = LayoutRect(paintInvalidationLogicalLeft, m_paintInvalidationLogicalTop, paintInvalidationLogicalRight - paintInvalidationLogicalLeft, m_paintInvalidationLogicalBottom - m_paintInvalidationLogicalTop);
     else
         paintInvalidationRect = LayoutRect(m_paintInvalidationLogicalTop, paintInvalidationLogicalLeft, m_paintInvalidationLogicalBottom - m_paintInvalidationLogicalTop, paintInvalidationLogicalRight - paintInvalidationLogicalLeft);

     // The paint invalidation rect may be split across columns, in which case adjustRectForColumns() will return the union.
     adjustRectForColumns(paintInvalidationRect);

     if (hasOverflowClip()) {
         // Adjust the paint invalidation rect for scroll offset
         paintInvalidationRect.move(-scrolledContentOffset());

         // Don't allow this rect to spill out of our overflow box.
         paintInvalidationRect.intersect(LayoutRect(LayoutPoint(), size()));
     }

     // Make sure the rect is still non-empty after intersecting for overflow above
     if (!paintInvalidationRect.isEmpty()) {
         // Hits in media/event-attributes.html
         DisableCompositingQueryAsserts disabler;

         invalidatePaintRectangle(paintInvalidationRect); // We need to do a partial paint invalidation of our content.
         if (hasReflection())
             invalidatePaintRectangle(reflectedRect(paintInvalidationRect));
     }

     m_paintInvalidationLogicalTop = 0;
     m_paintInvalidationLogicalBottom = 0;
 }

 void RenderBlockFlow::paintFloats(PaintInfo& paintInfo, const LayoutPoint& paintOffset, bool preservePhase)
 {
     BlockFlowPainter(*this).paintFloats(paintInfo, paintOffset, preservePhase);
 }

 void RenderBlockFlow::clipOutFloatingObjects(const RenderBlock* rootBlock, const PaintInfo* paintInfo, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock) const
 {
     if (m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         FloatingObjectSetIterator end = floatingObjectSet.end();
         for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
             FloatingObject* floatingObject = it->get();
             LayoutRect floatBox(offsetFromRootBlock.width() + xPositionForFloatIncludingMargin(floatingObject),
                 offsetFromRootBlock.height() + yPositionForFloatIncludingMargin(floatingObject),
                 floatingObject->renderer()->width(), floatingObject->renderer()->height());
             rootBlock->flipForWritingMode(floatBox);
             floatBox.move(rootBlockPhysicalPosition.x(), rootBlockPhysicalPosition.y());
             paintInfo->context->clipOut(pixelSnappedIntRect(floatBox));
         }
     }
 }

 void RenderBlockFlow::clearFloats(EClear clear)
 {
     positionNewFloats();
     // set y position
     LayoutUnit newY = 0;
     switch (clear) {
     case CLEFT:
         newY = lowestFloatLogicalBottom(FloatingObject::FloatLeft);
         break;
     case CRIGHT:
         newY = lowestFloatLogicalBottom(FloatingObject::FloatRight);
         break;
     case CBOTH:
         newY = lowestFloatLogicalBottom();
     default:
         break;
     }
     if (height() < newY)
         setLogicalHeight(newY);
 }

 bool RenderBlockFlow::containsFloat(RenderBox* renderer) const
 {
     return m_floatingObjects && m_floatingObjects->set().contains<FloatingObjectHashTranslator>(renderer);
 }

 void RenderBlockFlow::removeFloatingObjects()
 {
     if (!m_floatingObjects)
         return;

     markSiblingsWithFloatsForLayout();

     m_floatingObjects->clear();
 }

 LayoutPoint RenderBlockFlow::flipFloatForWritingModeForChild(const FloatingObject* child, const LayoutPoint& point) const
 {
     if (!style()->isFlippedBlocksWritingMode())
         return point;

     // This is similar to RenderBox::flipForWritingModeForChild. We have to subtract out our left/top offsets twice, since
     // it's going to get added back in. We hide this complication here so that the calling code looks normal for the unflipped
     // case.
     if (isHorizontalWritingMode())
         return LayoutPoint(point.x(), point.y() + height() - child->renderer()->height() - 2 * yPositionForFloatIncludingMargin(child));
     return LayoutPoint(point.x() + width() - child->renderer()->width() - 2 * xPositionForFloatIncludingMargin(child), point.y());
 }

 LayoutUnit RenderBlockFlow::logicalLeftOffsetForPositioningFloat(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining) const
 {
     LayoutUnit offset = fixedOffset;
     if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
         offset = m_floatingObjects->logicalLeftOffsetForPositioningFloat(fixedOffset, logicalTop, heightRemaining);
     return adjustLogicalLeftOffsetForLine(offset, applyTextIndent);
 }

 LayoutUnit RenderBlockFlow::logicalRightOffsetForPositioningFloat(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining) const
 {
     LayoutUnit offset = fixedOffset;
     if (m_floatingObjects && m_floatingObjects->hasRightObjects())
         offset = m_floatingObjects->logicalRightOffsetForPositioningFloat(fixedOffset, logicalTop, heightRemaining);
     return adjustLogicalRightOffsetForLine(offset, applyTextIndent);
 }

 LayoutUnit RenderBlockFlow::adjustLogicalLeftOffsetForLine(LayoutUnit offsetFromFloats, bool applyTextIndent) const
 {
     LayoutUnit left = offsetFromFloats;

     if (applyTextIndent && style()->isLeftToRightDirection())
         left += textIndentOffset();

     return left;
 }

 LayoutUnit RenderBlockFlow::adjustLogicalRightOffsetForLine(LayoutUnit offsetFromFloats, bool applyTextIndent) const
 {
     LayoutUnit right = offsetFromFloats;

     if (applyTextIndent && !style()->isLeftToRightDirection())
         right -= textIndentOffset();

     return right;
 }

 LayoutPoint RenderBlockFlow::computeLogicalLocationForFloat(const FloatingObject* floatingObject, LayoutUnit logicalTopOffset) const
 {
     RenderBox* childBox = floatingObject->renderer();
     LayoutUnit logicalLeftOffset = logicalLeftOffsetForContent(); // Constant part of left offset.
     LayoutUnit logicalRightOffset; // Constant part of right offset.
     logicalRightOffset = logicalRightOffsetForContent();

     LayoutUnit floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset); // The width we look for.

     LayoutUnit floatLogicalLeft;

     bool insideFlowThread = flowThreadContainingBlock();

     if (childBox->style()->floating() == LeftFloat) {
         LayoutUnit heightRemainingLeft = 1;
         LayoutUnit heightRemainingRight = 1;
         floatLogicalLeft = logicalLeftOffsetForPositioningFloat(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
         while (logicalRightOffsetForPositioningFloat(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight) - floatLogicalLeft < floatLogicalWidth) {
             logicalTopOffset += std::min(heightRemainingLeft, heightRemainingRight);
             floatLogicalLeft = logicalLeftOffsetForPositioningFloat(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft);
             if (insideFlowThread) {
                 // Have to re-evaluate all of our offsets, since they may have changed.
                 logicalRightOffset = logicalRightOffsetForContent(); // Constant part of right offset.
                 logicalLeftOffset = logicalLeftOffsetForContent(); // Constant part of left offset.
                 floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
             }
         }
         floatLogicalLeft = std::max(logicalLeftOffset - borderAndPaddingLogicalLeft(), floatLogicalLeft);
     } else {
         LayoutUnit heightRemainingLeft = 1;
         LayoutUnit heightRemainingRight = 1;
         floatLogicalLeft = logicalRightOffsetForPositioningFloat(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
         while (floatLogicalLeft - logicalLeftOffsetForPositioningFloat(logicalTopOffset, logicalLeftOffset, false, &heightRemainingLeft) < floatLogicalWidth) {
             logicalTopOffset += std::min(heightRemainingLeft, heightRemainingRight);
             floatLogicalLeft = logicalRightOffsetForPositioningFloat(logicalTopOffset, logicalRightOffset, false, &heightRemainingRight);
             if (insideFlowThread) {
                 // Have to re-evaluate all of our offsets, since they may have changed.
                 logicalRightOffset = logicalRightOffsetForContent(); // Constant part of right offset.
                 logicalLeftOffset = logicalLeftOffsetForContent(); // Constant part of left offset.
                 floatLogicalWidth = std::min(logicalWidthForFloat(floatingObject), logicalRightOffset - logicalLeftOffset);
             }
         }
         // Use the original width of the float here, since the local variable
         // |floatLogicalWidth| was capped to the available line width. See
         // fast/block/float/clamped-right-float.html.
         floatLogicalLeft -= logicalWidthForFloat(floatingObject);
     }

     return LayoutPoint(floatLogicalLeft, logicalTopOffset);
 }

 FloatingObject* RenderBlockFlow::insertFloatingObject(RenderBox* floatBox)
 {
     ASSERT(floatBox->isFloating());

     // Create the list of special objects if we don't aleady have one
     if (!m_floatingObjects) {
         createFloatingObjects();
     } else {
         // Don't insert the object again if it's already in the list
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(floatBox);
         if (it != floatingObjectSet.end())
             return it->get();
     }

     // Create the special object entry & append it to the list

     OwnPtr<FloatingObject> newObj = FloatingObject::create(floatBox);

     // Our location is irrelevant if we're unsplittable or no pagination is in effect.
     // Just go ahead and lay out the float.
     bool isChildRenderBlock = floatBox->isRenderBlock();
     if (isChildRenderBlock && !floatBox->needsLayout() && view()->layoutState()->pageLogicalHeightChanged())
         floatBox->setChildNeedsLayout(MarkOnlyThis);

     bool needsBlockDirectionLocationSetBeforeLayout = isChildRenderBlock && view()->layoutState()->needsBlockDirectionLocationSetBeforeLayout();
     if (!needsBlockDirectionLocationSetBeforeLayout || isWritingModeRoot()) { // We are unsplittable if we're a block flow root.
         floatBox->layoutIfNeeded();
     } else {
         floatBox->updateLogicalWidth();
         floatBox->computeAndSetBlockDirectionMargins(this);
     }

     setLogicalWidthForFloat(newObj.get(), logicalWidthForChild(floatBox) + marginStartForChild(floatBox) + marginEndForChild(floatBox));

     return m_floatingObjects->add(newObj.release());
 }

 void RenderBlockFlow::removeFloatingObject(RenderBox* floatBox)
 {
     if (m_floatingObjects) {
         const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
         FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(floatBox);
         if (it != floatingObjectSet.end()) {
             FloatingObject* floatingObject = it->get();
             if (childrenInline()) {
                 LayoutUnit logicalTop = logicalTopForFloat(floatingObject);
                 LayoutUnit logicalBottom = logicalBottomForFloat(floatingObject);

                 // Fix for https://bugs.webkit.org/show_bug.cgi?id=54995.
                 if (logicalBottom < 0 || logicalBottom < logicalTop || logicalTop == LayoutUnit::max()) {
                     logicalBottom = LayoutUnit::max();
                 } else {
                     // Special-case zero- and less-than-zero-height floats: those don't touch
                     // the line that they're on, but it still needs to be dirtied. This is
                     // accomplished by pretending they have a height of 1.
                     logicalBottom = std::max(logicalBottom, logicalTop + 1);
                 }
                 if (floatingObject->originatingLine()) {
                     if (!selfNeedsLayout()) {
                         ASSERT(floatingObject->originatingLine()->renderer() == this);
                         floatingObject->originatingLine()->markDirty();
                     }
 #if ENABLE(ASSERT)
                     floatingObject->setOriginatingLine(0);
 #endif
                 }
                 markLinesDirtyInBlockRange(0, logicalBottom);
             }
             m_floatingObjects->remove(floatingObject);
         }
     }
 }

 void RenderBlockFlow::removeFloatingObjectsBelow(FloatingObject* lastFloat, int logicalOffset)
 {
     if (!containsFloats())
         return;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObject* curr = floatingObjectSet.last().get();
     while (curr != lastFloat && (!curr->isPlaced() || logicalTopForFloat(curr) >= logicalOffset)) {
         m_floatingObjects->remove(curr);
         if (floatingObjectSet.isEmpty())
             break;
         curr = floatingObjectSet.last().get();
     }
 }

 bool RenderBlockFlow::positionNewFloats()
 {
     if (!m_floatingObjects)
         return false;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     if (floatingObjectSet.isEmpty())
         return false;

     // If all floats have already been positioned, then we have no work to do.
     if (floatingObjectSet.last()->isPlaced())
         return false;

     // Move backwards through our floating object list until we find a float that has
     // already been positioned. Then we'll be able to move forward, positioning all of
     // the new floats that need it.
     FloatingObjectSetIterator it = floatingObjectSet.end();
     --it; // Go to last item.
     FloatingObjectSetIterator begin = floatingObjectSet.begin();
     FloatingObject* lastPlacedFloatingObject = 0;
     while (it != begin) {
         --it;
         if ((*it)->isPlaced()) {
             lastPlacedFloatingObject = it->get();
             ++it;
             break;
         }
     }

     LayoutUnit logicalTop = logicalHeight();

     // The float cannot start above the top position of the last positioned float.
     if (lastPlacedFloatingObject)
         logicalTop = std::max(logicalTopForFloat(lastPlacedFloatingObject), logicalTop);

     FloatingObjectSetIterator end = floatingObjectSet.end();
     // Now walk through the set of unpositioned floats and place them.
     for (; it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         // The containing block is responsible for positioning floats, so if we have floats in our
         // list that come from somewhere else, do not attempt to position them.
         if (floatingObject->renderer()->containingBlock() != this)
             continue;

         RenderBox* childBox = floatingObject->renderer();

         // FIXME Investigate if this can be removed. crbug.com/370006
         childBox->setMayNeedPaintInvalidation(true);

         LayoutUnit childLogicalLeftMargin = style()->isLeftToRightDirection() ? marginStartForChild(childBox) : marginEndForChild(childBox);
         if (childBox->style()->clear() & CLEFT)
             logicalTop = std::max(lowestFloatLogicalBottom(FloatingObject::FloatLeft), logicalTop);
         if (childBox->style()->clear() & CRIGHT)
             logicalTop = std::max(lowestFloatLogicalBottom(FloatingObject::FloatRight), logicalTop);

         LayoutPoint floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, logicalTop);

         setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

         setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
         setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

         SubtreeLayoutScope layoutScope(*childBox);
         LayoutState* layoutState = view()->layoutState();
         bool isPaginated = layoutState->isPaginated();
         if (isPaginated && !childBox->needsLayout())
             childBox->markForPaginationRelayoutIfNeeded(layoutScope);

         childBox->layoutIfNeeded();

         if (isPaginated) {
             // If we are unsplittable and don't fit, then we need to move down.
             // We include our margins as part of the unsplittable area.
             LayoutUnit newLogicalTop = adjustForUnsplittableChild(childBox, floatLogicalLocation.y(), true);

             // See if we have a pagination strut that is making us move down further.
             // Note that an unsplittable child can't also have a pagination strut, so this is
             // exclusive with the case above.
             RenderBlockFlow* childBlockFlow = childBox->isRenderBlockFlow() ? toRenderBlockFlow(childBox) : 0;
             if (childBlockFlow && childBlockFlow->paginationStrut()) {
                 newLogicalTop += childBlockFlow->paginationStrut();
                 childBlockFlow->setPaginationStrut(0);
             }

             if (newLogicalTop != floatLogicalLocation.y()) {
                 floatingObject->setPaginationStrut(newLogicalTop - floatLogicalLocation.y());

                 floatLogicalLocation = computeLogicalLocationForFloat(floatingObject, newLogicalTop);
                 setLogicalLeftForFloat(floatingObject, floatLogicalLocation.x());

                 setLogicalLeftForChild(childBox, floatLogicalLocation.x() + childLogicalLeftMargin);
                 setLogicalTopForChild(childBox, floatLogicalLocation.y() + marginBeforeForChild(childBox));

                 if (childBox->isRenderBlock())
                     childBox->setChildNeedsLayout(MarkOnlyThis);
                 childBox->layoutIfNeeded();
             }
         }

         setLogicalTopForFloat(floatingObject, floatLogicalLocation.y());

         setLogicalHeightForFloat(floatingObject, logicalHeightForChild(childBox) + marginBeforeForChild(childBox) + marginAfterForChild(childBox));

         m_floatingObjects->addPlacedObject(floatingObject);

         if (ShapeOutsideInfo* shapeOutside = childBox->shapeOutsideInfo())
             shapeOutside->setReferenceBoxLogicalSize(logicalSizeForChild(childBox));
     }
     return true;
 }

 bool RenderBlockFlow::hasOverhangingFloat(RenderBox* renderer)
 {
     if (!m_floatingObjects || hasColumns() || !parent())
         return false;

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator it = floatingObjectSet.find<FloatingObjectHashTranslator>(renderer);
     if (it == floatingObjectSet.end())
         return false;

     return logicalBottomForFloat(it->get()) > logicalHeight();
 }

 void RenderBlockFlow::addIntrudingFloats(RenderBlockFlow* prev, LayoutUnit logicalLeftOffset, LayoutUnit logicalTopOffset)
 {
     ASSERT(!avoidsFloats());

     // If we create our own block formatting context then our contents don't interact with floats outside it, even those from our parent.
     if (createsBlockFormattingContext())
         return;

     // If the parent or previous sibling doesn't have any floats to add, don't bother.
     if (!prev->m_floatingObjects)
         return;

     logicalLeftOffset += marginLogicalLeft();

     const FloatingObjectSet& prevSet = prev->m_floatingObjects->set();
     FloatingObjectSetIterator prevEnd = prevSet.end();
     for (FloatingObjectSetIterator prevIt = prevSet.begin(); prevIt != prevEnd; ++prevIt) {
         FloatingObject* floatingObject = prevIt->get();
         if (logicalBottomForFloat(floatingObject) > logicalTopOffset) {
             if (!m_floatingObjects || !m_floatingObjects->set().contains(floatingObject)) {
                 // We create the floating object list lazily.
                 if (!m_floatingObjects)
                     createFloatingObjects();

                 // Applying the child's margin makes no sense in the case where the child was passed in.
                 // since this margin was added already through the modification of the |logicalLeftOffset| variable
                 // above. |logicalLeftOffset| will equal the margin in this case, so it's already been taken
                 // into account. Only apply this code if prev is the parent, since otherwise the left margin
                 // will get applied twice.
                 LayoutSize offset = isHorizontalWritingMode()
                     ? LayoutSize(logicalLeftOffset - (prev != parent() ? prev->marginLeft() : LayoutUnit()), logicalTopOffset)
                     : LayoutSize(logicalTopOffset, logicalLeftOffset - (prev != parent() ? prev->marginTop() : LayoutUnit()));

                 m_floatingObjects->add(floatingObject->copyToNewContainer(offset));
             }
         }
     }
 }

 void RenderBlockFlow::addOverhangingFloats(RenderBlockFlow* child, bool makeChildPaintOtherFloats)
 {
     // Prevent floats from being added to the canvas by the root element, e.g., <html>.
     if (!child->containsFloats() || child->isRenderRegion() || child->createsBlockFormattingContext())
         return;

     LayoutUnit childLogicalTop = child->logicalTop();
     LayoutUnit childLogicalLeft = child->logicalLeft();

     // Floats that will remain the child's responsibility to paint should factor into its
     // overflow.
     FloatingObjectSetIterator childEnd = child->m_floatingObjects->set().end();
     for (FloatingObjectSetIterator childIt = child->m_floatingObjects->set().begin(); childIt != childEnd; ++childIt) {
         FloatingObject* floatingObject = childIt->get();
         LayoutUnit logicalBottomForFloat = std::min(this->logicalBottomForFloat(floatingObject), LayoutUnit::max() - childLogicalTop);
         LayoutUnit logicalBottom = childLogicalTop + logicalBottomForFloat;

         if (logicalBottom > logicalHeight()) {
             // If the object is not in the list, we add it now.
             if (!containsFloat(floatingObject->renderer())) {
                 LayoutSize offset = isHorizontalWritingMode() ? LayoutSize(-childLogicalLeft, -childLogicalTop) : LayoutSize(-childLogicalTop, -childLogicalLeft);
                 bool shouldPaint = false;

                 // The nearest enclosing layer always paints the float (so that zindex and stacking
                 // behaves properly). We always want to propagate the desire to paint the float as
                 // far out as we can, to the outermost block that overlaps the float, stopping only
                 // if we hit a self-painting layer boundary.
                 if (floatingObject->renderer()->enclosingFloatPaintingLayer() == enclosingFloatPaintingLayer()) {
                     floatingObject->setShouldPaint(false);
                     shouldPaint = true;
                 }
                 // We create the floating object list lazily.
                 if (!m_floatingObjects)
                     createFloatingObjects();

                 m_floatingObjects->add(floatingObject->copyToNewContainer(offset, shouldPaint, true));
             }
         } else {
             if (makeChildPaintOtherFloats && !floatingObject->shouldPaint() && !floatingObject->renderer()->hasSelfPaintingLayer()
                 && floatingObject->renderer()->isDescendantOf(child) && floatingObject->renderer()->enclosingFloatPaintingLayer() == child->enclosingFloatPaintingLayer()) {
                 // The float is not overhanging from this block, so if it is a descendant of the child, the child should
                 // paint it (the other case is that it is intruding into the child), unless it has its own layer or enclosing
                 // layer.
                 // If makeChildPaintOtherFloats is false, it means that the child must already know about all the floats
                 // it should paint.
                 floatingObject->setShouldPaint(true);
             }

             // Since the float doesn't overhang, it didn't get put into our list. We need to go ahead and add its overflow in to the
             // child now.
             if (floatingObject->isDescendant())
                 child->addOverflowFromChild(floatingObject->renderer(), LayoutSize(xPositionForFloatIncludingMargin(floatingObject), yPositionForFloatIncludingMargin(floatingObject)));
         }
     }
 }

 LayoutUnit RenderBlockFlow::lowestFloatLogicalBottom(FloatingObject::Type floatType) const
 {
     if (!m_floatingObjects)
         return 0;

     return m_floatingObjects->lowestFloatLogicalBottom(floatType);
 }

 LayoutUnit RenderBlockFlow::nextFloatLogicalBottomBelow(LayoutUnit logicalHeight, ShapeOutsideFloatOffsetMode offsetMode) const
 {
     if (!m_floatingObjects)
         return logicalHeight;

     LayoutUnit logicalBottom;
     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator end = floatingObjectSet.end();
     for (FloatingObjectSetIterator it = floatingObjectSet.begin(); it != end; ++it) {
         FloatingObject* floatingObject = it->get();
         LayoutUnit floatLogicalBottom = logicalBottomForFloat(floatingObject);
         ShapeOutsideInfo* shapeOutside = floatingObject->renderer()->shapeOutsideInfo();
         if (shapeOutside && (offsetMode == ShapeOutsideFloatShapeOffset)) {
             LayoutUnit shapeLogicalBottom = logicalTopForFloat(floatingObject) + marginBeforeForChild(floatingObject->renderer()) + shapeOutside->shapeLogicalBottom();
             // Use the shapeLogicalBottom unless it extends outside of the margin box, in which case it is clipped.
             if (shapeLogicalBottom < floatLogicalBottom)
                 floatLogicalBottom = shapeLogicalBottom;
         }
         if (floatLogicalBottom > logicalHeight)
             logicalBottom = logicalBottom ? std::min(floatLogicalBottom, logicalBottom) : floatLogicalBottom;
     }

     return logicalBottom;
 }

 bool RenderBlockFlow::hitTestFloats(const HitTestRequest& request, HitTestResult& result, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset)
 {
     if (!m_floatingObjects)
         return false;

     LayoutPoint adjustedLocation = accumulatedOffset;
     if (isRenderView()) {
         adjustedLocation += toLayoutSize(LayoutPoint(toRenderView(this)->frameView()->scrollPositionDouble()));
     }

     const FloatingObjectSet& floatingObjectSet = m_floatingObjects->set();
     FloatingObjectSetIterator begin = floatingObjectSet.begin();
     for (FloatingObjectSetIterator it = floatingObjectSet.end(); it != begin;) {
         --it;
         FloatingObject* floatingObject = it->get();
         if (floatingObject->shouldPaint() && !floatingObject->renderer()->hasSelfPaintingLayer()) {
             LayoutUnit xOffset = xPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer()->x();
             LayoutUnit yOffset = yPositionForFloatIncludingMargin(floatingObject) - floatingObject->renderer()->y();
             LayoutPoint childPoint = flipFloatForWritingModeForChild(floatingObject, adjustedLocation + LayoutSize(xOffset, yOffset));
             if (floatingObject->renderer()->hitTest(request, result, locationInContainer, childPoint)) {
                 updateHitTestResult(result, locationInContainer.point() - toLayoutSize(childPoint));
                 return true;
             }
         }
     }

     return false;
 }

 LayoutUnit RenderBlockFlow::logicalLeftFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit logicalHeight) const
 {
     if (m_floatingObjects && m_floatingObjects->hasLeftObjects())
         return m_floatingObjects->logicalLeftOffset(fixedOffset, logicalTop, logicalHeight);

     return fixedOffset;
 }

 LayoutUnit RenderBlockFlow::logicalRightFloatOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, LayoutUnit logicalHeight) const
 {
     if (m_floatingObjects && m_floatingObjects->hasRightObjects())
         return m_floatingObjects->logicalRightOffset(fixedOffset, logicalTop, logicalHeight);

     return fixedOffset;
 }

 GapRects RenderBlockFlow::inlineSelectionGaps(const RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock,
     LayoutUnit& lastLogicalTop, LayoutUnit& lastLogicalLeft, LayoutUnit& lastLogicalRight, const PaintInfo* paintInfo) const
 {
     GapRects result;

     bool containsStart = selectionState() == SelectionStart || selectionState() == SelectionBoth;

     if (!firstLineBox()) {
         if (containsStart) {
             // Go ahead and update our lastLogicalTop to be the bottom of the block.  <hr>s or empty blocks with height can trip this
             // case.
             lastLogicalTop = rootBlock->blockDirectionOffset(offsetFromRootBlock) + logicalHeight();
             lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, logicalHeight());
             lastLogicalRight = logicalRightSelectionOffset(rootBlock, logicalHeight());
         }
         return result;
     }

     RootInlineBox* lastSelectedLine = 0;
     RootInlineBox* curr;
     for (curr = firstRootBox(); curr && !curr->hasSelectedChildren(); curr = curr->nextRootBox()) { }

     // Now paint the gaps for the lines.
     for (; curr && curr->hasSelectedChildren(); curr = curr->nextRootBox()) {
         LayoutUnit selTop =  curr->selectionTopAdjustedForPrecedingBlock();
         LayoutUnit selHeight = curr->selectionHeightAdjustedForPrecedingBlock();

         if (!containsStart && !lastSelectedLine && selectionState() != SelectionStart && selectionState() != SelectionBoth) {
             result.uniteCenter(blockSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, lastLogicalTop,
                 lastLogicalLeft, lastLogicalRight, selTop, paintInfo));
         }

         LayoutRect logicalRect(curr->logicalLeft(), selTop, curr->logicalWidth(), selTop + selHeight);
         logicalRect.move(isHorizontalWritingMode() ? offsetFromRootBlock : offsetFromRootBlock.transposedSize());
         LayoutRect physicalRect = rootBlock->logicalRectToPhysicalRect(rootBlockPhysicalPosition, logicalRect);
         if (!paintInfo || (isHorizontalWritingMode() && physicalRect.y() < paintInfo->rect.maxY() && physicalRect.maxY() > paintInfo->rect.y())
             || (!isHorizontalWritingMode() && physicalRect.x() < paintInfo->rect.maxX() && physicalRect.maxX() > paintInfo->rect.x()))
             result.unite(curr->lineSelectionGap(rootBlock, rootBlockPhysicalPosition, offsetFromRootBlock, selTop, selHeight, paintInfo));

         lastSelectedLine = curr;
     }

     if (containsStart && !lastSelectedLine) {
         // VisibleSelection must start just after our last line.
         lastSelectedLine = lastRootBox();
     }

     if (lastSelectedLine && selectionState() != SelectionEnd && selectionState() != SelectionBoth) {
         // Go ahead and update our lastY to be the bottom of the last selected line.
         lastLogicalTop = rootBlock->blockDirectionOffset(offsetFromRootBlock) + lastSelectedLine->selectionBottom();
         lastLogicalLeft = logicalLeftSelectionOffset(rootBlock, lastSelectedLine->selectionBottom());
         lastLogicalRight = logicalRightSelectionOffset(rootBlock, lastSelectedLine->selectionBottom());
     }
     return result;
 }

 void RenderBlockFlow::setPaginationStrut(LayoutUnit strut)
 {
     if (!m_rareData) {
         if (!strut)
             return;
         m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
     }
     m_rareData->m_paginationStrut = strut;
 }

 bool RenderBlockFlow::avoidsFloats() const
 {
     // Floats can't intrude into our box if we have a non-auto column count or width.
     // Note: we need to use RenderBox::avoidsFloats here since RenderBlock::avoidsFloats is always true.
     return RenderBox::avoidsFloats() || !style()->hasAutoColumnCount() || !style()->hasAutoColumnWidth();
 }

 LayoutUnit RenderBlockFlow::logicalLeftSelectionOffset(const RenderBlock* rootBlock, LayoutUnit position) const
 {
     LayoutUnit logicalLeft = logicalLeftOffsetForLine(position, false);
     if (logicalLeft == logicalLeftOffsetForContent())
         return RenderBlock::logicalLeftSelectionOffset(rootBlock, position);

     const RenderBlock* cb = this;
     while (cb != rootBlock) {
         logicalLeft += cb->logicalLeft();
         cb = cb->containingBlock();
     }
     return logicalLeft;
 }

 LayoutUnit RenderBlockFlow::logicalRightSelectionOffset(const RenderBlock* rootBlock, LayoutUnit position) const
 {
     LayoutUnit logicalRight = logicalRightOffsetForLine(position, false);
     if (logicalRight == logicalRightOffsetForContent())
         return RenderBlock::logicalRightSelectionOffset(rootBlock, position);

     const RenderBlock* cb = this;
     while (cb != rootBlock) {
         logicalRight += cb->logicalLeft();
         cb = cb->containingBlock();
     }
     return logicalRight;
 }

 RootInlineBox* RenderBlockFlow::createRootInlineBox()
 {
     return new RootInlineBox(*this);
 }

 bool RenderBlockFlow::isPagedOverflow(const RenderStyle* style)
 {
     return style->isOverflowPaged() && node() != document().viewportDefiningElement();
 }

 RenderBlockFlow::FlowThreadType RenderBlockFlow::flowThreadType(const RenderStyle* style)
 {
     if (isPagedOverflow(style))
         return PagedFlowThread;
     if (style->specifiesColumns())
         return MultiColumnFlowThread;
     return NoFlowThread;
 }

 RenderMultiColumnFlowThread* RenderBlockFlow::createMultiColumnFlowThread(FlowThreadType type)
 {
     switch (type) {
     case MultiColumnFlowThread:
         return RenderMultiColumnFlowThread::createAnonymous(document(), style());
     case PagedFlowThread:
         // Paged overflow is currently done using the multicol implementation.
         return RenderPagedFlowThread::createAnonymous(document(), style());
     default:
         ASSERT_NOT_REACHED();
         return nullptr;
     }
 }

 void RenderBlockFlow::createOrDestroyMultiColumnFlowThreadIfNeeded(const RenderStyle* oldStyle)
 {
     if (!document().regionBasedColumnsEnabled())
         return;

     // Paged overflow trumps multicol in this implementation. Ideally, it should be possible to have
     // both paged overflow and multicol on the same element, but then we need two flow
     // threads. Anyway, this is nothing to worry about until we can actually nest multicol properly
     // inside other fragmentation contexts.
     FlowThreadType type = flowThreadType(style());

     if (multiColumnFlowThread()) {
         ASSERT(oldStyle);
         if (type != flowThreadType(oldStyle)) {
             // If we're no longer to be multicol/paged, destroy the flow thread. Also destroy it
             // when switching between multicol and paged, since that affects the column set
             // structure (multicol containers may have spanners, paged containers may not).
             multiColumnFlowThread()->evacuateAndDestroy();
             ASSERT(!multiColumnFlowThread());
         }
     }

     if (type == NoFlowThread || multiColumnFlowThread())
         return;

     RenderMultiColumnFlowThread* flowThread = createMultiColumnFlowThread(type);
     addChild(flowThread);
     flowThread->populate();
     RenderBlockFlowRareData& rareData = ensureRareData();
     ASSERT(!rareData.m_multiColumnFlowThread);
     rareData.m_multiColumnFlowThread = flowThread;
 }

 RenderBlockFlow::RenderBlockFlowRareData& RenderBlockFlow::ensureRareData()
 {
     if (m_rareData)
         return *m_rareData;

     m_rareData = adoptPtrWillBeNoop(new RenderBlockFlowRareData(this));
     return *m_rareData;
 }

 void RenderBlockFlow::positionDialog()
 {
     HTMLDialogElement* dialog = toHTMLDialogElement(node());
     if (dialog->centeringMode() == HTMLDialogElement::NotCentered)
         return;

     bool canCenterDialog = (style()->position() == AbsolutePosition || style()->position() == FixedPosition)
         && style()->hasAutoTopAndBottom();

     if (dialog->centeringMode() == HTMLDialogElement::Centered) {
         if (canCenterDialog)
             setY(dialog->centeredPosition());
         return;
     }

     ASSERT(dialog->centeringMode() == HTMLDialogElement::NeedsCentering);
     if (!canCenterDialog) {
         dialog->setNotCentered();
         return;
     }

     FrameView* frameView = document().view();
     LayoutUnit top = (style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height();
     int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
     if (height() < visibleHeight)
         top += (visibleHeight - height()) / 2;
     setY(top);
     dialog->setCentered(top);
 }

 } // namespace blink