Prepare RenderLayerBacking and RenderLayerCompositor for subpixel layout

Prepare RenderLayerBacking and RenderLayerCompositor for subpixel layout
https://bugs.webkit.org/show_bug.cgi?id=78630

Reviewed by Simon Fraser.

In our transition to subpixel layout in the render tree, we continue to pass RenderLayerBacking
and RenderLayerCompositor integer (pixel) sizes and positions. This patch moves nearly all
methods and members on these two classes back to integers, and applies pixel snapping logic to
LayoutUnits pulled in.

No new tests. No change in behavior.

* rendering/RenderBox.h:
(WebCore::RenderBox::pixelSnappedLayoutOverflowRect): Convenience function for getting pixel
snapped overflow bounds.
* rendering/RenderLayerBacking.cpp:
(WebCore):
(WebCore::RenderLayerBacking::updateCompositedBounds): Switch to integers and pixel snapping the
clipping bounds.
(WebCore::clipBox): Returns a pixel snapped rect.
(WebCore::RenderLayerBacking::updateGraphicsLayerGeometry): Using pixelSnappedLayerCoords. Removing
pixelSnappedIntRect calls to clipBox since this is now an IntRect.
(WebCore::RenderLayerBacking::computeTransformOrigin): Switching to operate on a pixel snapped rect.
(WebCore::RenderLayerBacking::computePerspectiveOrigin): Ditto.
(WebCore::RenderLayerBacking::contentOffsetInCompostingLayer): Returns a size based on m_compositingBounds,
which is now an IntSize.
(WebCore::RenderLayerBacking::contentsBox): Switching to use pixel snapped values from the render tree.
(WebCore::RenderLayerBacking::setContentsNeedDisplayInRect): This now takes in and outputs integers.
(WebCore::RenderLayerBacking::paintIntoLayer): Uses a pixel snapped rect for the dirty rect.
(WebCore::paintScrollbar): Scrollbars are Widgets & painted natively, so they should use integers.
(WebCore::RenderLayerBacking::paintContents): We now properly take in an integer clip rect, as it's
used for the scrollbars.
(WebCore::RenderLayerBacking::startAnimation): Using pixel snapped values for animations and transitions.
(WebCore::RenderLayerBacking::startTransition): Ditto.
(WebCore::RenderLayerBacking::compositedBounds): Composited bounds are now properly stored as integers.
(WebCore::RenderLayerBacking::setCompositedBounds): Ditto.
* rendering/RenderLayerBacking.h:
(RenderLayerBacking):
* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::calculateCompositedBounds): Composited bounds are pixel snapped, but
we use LayoutUnits up until we snap and return.
(WebCore::RenderLayerCompositor::addToOverlapMap): Overlap mapping uses our integer positions. Switching
it back to operating on them.
(WebCore::RenderLayerCompositor::addToOverlapMapRecursive): Ditto.
(WebCore::RenderLayerCompositor::overlapsCompositedLayers): Ditto.
(WebCore::RenderLayerCompositor::computeCompositingRequirements): Using integers.
(WebCore::RenderLayerCompositor::frameViewDidChangeLocation): FrameViews are on integer bounds. We now
properly use these as integers.
(WebCore::RenderLayerCompositor::frameViewDidScroll): Ditto.
(WebCore::RenderLayerCompositor::recursiveRepaintLayerRect): Switching to use integers and
pixelSnappedLayerCoords.
(WebCore::RenderLayerCompositor::repaintCompositedLayersAbsoluteRect): Ditto.
(WebCore::RenderLayerCompositor::updateRootLayerPosition): Using integer positions, which are what
the apis used already returned.
(WebCore::RenderLayerCompositor::requiresCompositingForPlugin): Using pixel snapped values.
(WebCore::RenderLayerCompositor::requiresCompositingForFrame): Ditto.
(WebCore::paintScrollbar): Scrollbars should always use integers.
(WebCore::RenderLayerCompositor::paintContents): Switching to use an integer clip rect.
(WebCore::RenderLayerCompositor::ensureRootLayer): Using values from new pixelSnappedLayoutOverflowRect
method on RenderBox to ensure we're using values that are pixel snapped to the proper location.
(WebCore::RenderLayerCompositor::destroyRootLayer): Properly calling scrollbar invalidation methods
with integers.
* rendering/RenderLayerCompositor.h:
(RenderLayerCompositor):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@107760 268f45cc-cd09-0410-ab3c-d52691b4dbfc