[wk2] Not updating tiled backing coverage when main frame scrollability changes
https://bugs.webkit.org/show_bug.cgi?id=116123
<rdar://problem/13836559>

Reviewed by Simon Fraser.

* WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.h:
(TiledCoreAnimationDrawingArea):
Add updateMainFrameClipsToExposedRect.

* WebProcess/WebPage/mac/TiledCoreAnimationDrawingArea.mm:
(WebKit::TiledCoreAnimationDrawingArea::TiledCoreAnimationDrawingArea):
(WebKit::TiledCoreAnimationDrawingArea::flushLayers):
Remove m_clipsToExposedRect. We don't actually need it.

(WebKit::TiledCoreAnimationDrawingArea::mainFrameScrollabilityChanged):
Call updateMainFrameClipsToExposedRect so that we can always update
tiled backing coverage and can factor out our calls to setClipsToExposedRect.

(WebKit::TiledCoreAnimationDrawingArea::updateMainFrameClipsToExposedRect):
Factor out setClipsToExposedRect calls to here, and also call
FrameView::adjustTiledBackingCoverage so that the FrameView's tiled
backing is informed to allow overdraw in the UI-process-scrolling case.

(WebKit::TiledCoreAnimationDrawingArea::setRootCompositingLayer):
Use updateMainFrameClipsToExposedRect.

Export FrameView::adjustTiledBackingCoverage.

* WebCore.exp.in:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150093 268f45cc-cd09-0410-ab3c-d52691b4dbfc