Fix usage of LayoutUnits and pixel snapping in RenderLayer

Fix usage of LayoutUnits and pixel snapping in RenderLayer
https://bugs.webkit.org/show_bug.cgi?id=82498

Reviewed by Julien Chaffraix.

Fix usage of subpixel types and snapping/rounding in RenderLayer in
preparation for turning on subpixel layout.

No new tests, no change in functionality.

* rendering/LayoutTypes.h:
(WebCore::pixelSnappedIntSize):
Add no-op implementation of pixelSnappedIntSize, will be replaced with a
real implementation once we make the switch.

* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::updateLayerPosition):
Snap RenderBox size when updating the size of the layer.

(WebCore::RenderLayer::resize):
Round position when setting the inline style during resize operation.

(WebCore::RenderLayer::scrollCornerRect):
Remove unnecessary pixelSnappedIntRect call.

(WebCore::RenderLayer::positionOverflowControls):
Remove unnecessary pixelSnappedIntRect call.

(WebCore::RenderLayer::scrollWidth):
(WebCore::RenderLayer::scrollHeight):
Fix implementation of scrollWidth and Height to pixel snap the values.

(WebCore::RenderLayer::computeScrollDimensions):
(WebCore::RenderLayer::paintResizer):
(WebCore::RenderLayer::hitTestOverflowControls):
Remove unnecessary pixelSnappedIntRect calls.

(WebCore::RenderLayer::paintLayerContents):
Pixel snap values just before painting (instead of earlier on).

(WebCore::RenderLayer::hitTest):
(WebCore::RenderLayer::hitTestContents):
Change to use subpixel types.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@112977 268f45cc-cd09-0410-ab3c-d52691b4dbfc