Subpixel rendering: Make GraphicsLayer::paintGraphicsLayerContents()'s cliprect Float...

Subpixel rendering: Make GraphicsLayer::paintGraphicsLayerContents()'s cliprect FloatRect based.
https://bugs.webkit.org/show_bug.cgi?id=128911

Reviewed by Simon Fraser.

Switching from IntRect to FloatRect makes device pixel position clipping possible.

Covered by existing tests.

* WebCore.exp.in:
* platform/graphics/GraphicsLayer.cpp:
(WebCore::GraphicsLayer::paintGraphicsLayerContents):
* platform/graphics/GraphicsLayer.h:
* platform/graphics/ca/GraphicsLayerCA.cpp:
(WebCore::GraphicsLayerCA::platformCALayerPaintContents):
* platform/graphics/ca/GraphicsLayerCA.h:
* platform/graphics/ca/PlatformCALayerClient.h:
* platform/graphics/ca/mac/TileController.h:
* platform/graphics/ca/mac/TileController.mm:
(WebCore::TileController::platformCALayerPaintContents):
* platform/graphics/mac/WebLayer.mm:
(WebCore::drawLayerContents):
(-[WebSimpleLayer drawInContext:]):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@164412 268f45cc-cd09-0410-ab3c-d52691b4dbfc