Merge 88496 - 2011-06-09 James Robinson <jamesr@chromium.org>

Merge 88496 - 2011-06-09  James Robinson  <jamesr@chromium.org>;

        Reviewed by Kenneth Russell.

        [chromium] Scissor rect not set for clipping layers set offscreen
        https://bugs.webkit.org/show_bug.cgi?id=62339

        Tests that a layer that should clip its children actually does clip even when scrolled offscreen.

        * platform/chromium/compositing/scissor-out-of-viewport-expected.png: Added.
        * platform/chromium/compositing/scissor-out-of-viewport-expected.txt: Added.
        * platform/chromium/compositing/scissor-out-of-viewport.html: Added.
2011-06-09  James Robinson  <jamesr@chromium.org>;

        Reviewed by Kenneth Russell.

        [chromium] Scissor rect not set for clipping layers set offscreen
        https://bugs.webkit.org/show_bug.cgi?id=62339

        We set a scissorRect on each layer, but only layers with masksToBounds and their descendants should actually set
        a scissor.  Layers that didn't need to scissor had empty scissorRects.  Unfortunately layers with masksToBounds
        and their descendants that are scrolled offscreen also end up with an empty clipped scissor rect.

        This patch sets an explicit bit on each layer that should scissor and then checks that bit instead of checking
        for an empty scissor rect at draw time.  RenderSurfaceChromiums have different requirements for
        setScissorToRect, so the old behavior is still available with a flag.  This can probably be cleaned up more.

        Test: platform/chromium/compositing/scissor-out-of-viewport.html

        * platform/graphics/chromium/LayerRendererChromium.cpp:
        (WebCore::LayerRendererChromium::updatePropertiesAndRenderSurfaces):
        (WebCore::LayerRendererChromium::drawLayer):
        (WebCore::LayerRendererChromium::setScissorToRect):
        * platform/graphics/chromium/LayerRendererChromium.h:
        * platform/graphics/chromium/RenderSurfaceChromium.cpp:
        (WebCore::RenderSurfaceChromium::draw):
        * platform/graphics/chromium/cc/CCLayerImpl.cpp:
        (WebCore::CCLayerImpl::CCLayerImpl):
        * platform/graphics/chromium/cc/CCLayerImpl.h:
        (WebCore::CCLayerImpl::setUsesLayerScissor):
        (WebCore::CCLayerImpl::usesLayerScissor):

BUG=84122
TBR=jamesr@chromium.org
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=88501