Subpixel rendering: Background clipping with subpixel behaves differently when composited.
https://bugs.webkit.org/show_bug.cgi?id=134422

Reviewed by Simon Fraser.

Adjust cliprect with the subpixel offset from the graphics layer the same way we do it for painting.
It ensures that cliprect starts from the right position when graphics layer is not on the same
coordinates as the associated render layer.

Source/WebCore:
Test: compositing/hidpi-compositing-layer-with-subpixel-offset-accumulation-clipping.html

* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::clipToRect):
(WebCore::RenderLayer::paintLayer):
(WebCore::RenderLayer::applyFilters):
(WebCore::RenderLayer::paintTransformedLayerIntoFragments):
(WebCore::RenderLayer::paintBackgroundForFragments):
(WebCore::RenderLayer::paintForegroundForFragments):
(WebCore::RenderLayer::paintForegroundForFragmentsWithPhase):
(WebCore::RenderLayer::paintOutlineForFragments):
(WebCore::RenderLayer::paintMaskForFragments):
(WebCore::RenderLayer::paintOverflowControlsForFragments):
(WebCore::RenderLayer::calculateClipRects):
* rendering/RenderLayer.h:

LayoutTests:
* compositing/hidpi-compositing-layer-with-subpixel-offset-accumulation-clipping-expected.html: Added.
* compositing/hidpi-compositing-layer-with-subpixel-offset-accumulation-clipping.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@170563 268f45cc-cd09-0410-ab3c-d52691b4dbfc