Make MultiColumnFragmentainerGroup::m_columnSet const.

Ideally, I'd like to get rid of the member altogether, but that would require a
lot of refactoring.

This is a preparatory patch for a fix for bug 604609.

BUG=604609

Review URL: https://codereview.chromium.org/1898293003

Cr-Commit-Position: refs/heads/master@{#388326}
diff --git a/third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp b/third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp
index 1ad819f..9c40e3d 100644
--- a/third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutMultiColumnSet.cpp
@@ -313,7 +313,7 @@
 
     bool changed = false;
     for (auto& group : m_fragmentainerGroups)
-        changed = group.recalculateColumnHeight() || changed;
+        changed = group.recalculateColumnHeight(*this) || changed;
     m_initialHeightCalculated = true;
     return changed;
 }
diff --git a/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp b/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
index e2fae00..855466f5 100644
--- a/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
+++ b/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
@@ -10,7 +10,7 @@
 
 namespace blink {
 
-MultiColumnFragmentainerGroup::MultiColumnFragmentainerGroup(LayoutMultiColumnSet& columnSet)
+MultiColumnFragmentainerGroup::MultiColumnFragmentainerGroup(const LayoutMultiColumnSet& columnSet)
     : m_columnSet(columnSet)
 {
 }
@@ -57,7 +57,7 @@
     }
 }
 
-bool MultiColumnFragmentainerGroup::recalculateColumnHeight()
+bool MultiColumnFragmentainerGroup::recalculateColumnHeight(LayoutMultiColumnSet& columnSet)
 {
     LayoutUnit oldColumnHeight = m_columnHeight;
 
@@ -66,18 +66,18 @@
     // Only the last row may have auto height, and thus be balanced. There are no good reasons to
     // balance the preceding rows, and that could potentially lead to an insane number of layout
     // passes as well.
-    if (isLastGroup() && m_columnSet.heightIsAuto()) {
+    if (isLastGroup() && columnSet.heightIsAuto()) {
         LayoutUnit newColumnHeight;
-        if (!m_columnSet.isInitialHeightCalculated()) {
+        if (!columnSet.isInitialHeightCalculated()) {
             // Initial balancing: Start with the lowest imaginable column height. Also calculate the
             // height of the tallest piece of unbreakable content. Columns should never get any
             // shorter than that (unless constrained by max-height). Propagate this to our
             // containing column set, in case there is an outer multicol container that also needs
             // to balance. After having calculated the initial column height, the multicol container
             // needs another layout pass with the column height that we just calculated.
-            InitialColumnHeightFinder initialHeightFinder(columnSet(), logicalTopInFlowThread(), logicalBottomInFlowThread());
+            InitialColumnHeightFinder initialHeightFinder(columnSet, logicalTopInFlowThread(), logicalBottomInFlowThread());
             LayoutUnit tallestUnbreakableLogicalHeight = initialHeightFinder.tallestUnbreakableLogicalHeight();
-            m_columnSet.propagateTallestUnbreakableLogicalHeight(tallestUnbreakableLogicalHeight);
+            columnSet.propagateTallestUnbreakableLogicalHeight(tallestUnbreakableLogicalHeight);
             newColumnHeight = std::max(initialHeightFinder.initialMinimalBalancedHeight(), tallestUnbreakableLogicalHeight);
         } else {
             // Rebalancing: After having laid out again, we'll need to rebalance if the height
diff --git a/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.h b/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.h
index e1ca9abfb..4f7df29 100644
--- a/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.h
+++ b/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.h
@@ -29,7 +29,7 @@
 class MultiColumnFragmentainerGroup {
     DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
 public:
-    MultiColumnFragmentainerGroup(LayoutMultiColumnSet&);
+    MultiColumnFragmentainerGroup(const LayoutMultiColumnSet&);
 
     const LayoutMultiColumnSet& columnSet() const { return m_columnSet; }
 
@@ -60,7 +60,7 @@
     LayoutUnit logicalHeightInFlowThread() const { return m_logicalBottomInFlowThread - m_logicalTopInFlowThread; }
 
     void resetColumnHeight();
-    bool recalculateColumnHeight();
+    bool recalculateColumnHeight(LayoutMultiColumnSet&);
 
     LayoutSize flowThreadTranslationAtOffset(LayoutUnit offsetInFlowThread) const;
     LayoutUnit columnLogicalTopForOffset(LayoutUnit offsetInFlowThread) const;
@@ -103,7 +103,7 @@
     // Get the first and the last column intersecting the specified visual rectangle.
     void columnIntervalForVisualRect(const LayoutRect&, unsigned& firstColumn, unsigned& lastColumn) const;
 
-    LayoutMultiColumnSet& m_columnSet;
+    const LayoutMultiColumnSet& m_columnSet;
 
     LayoutUnit m_logicalTop;
     LayoutUnit m_logicalTopInFlowThread;