Reviewed by Dan Bernstein.

        Disable ShadowBlur shadow drawing in accelerated contexts
        https://bugs.webkit.org/show_bug.cgi?id=56392

        When drawing into a graphics context that is accelerated, don't use
        ShadowBlur, because it may be slower.

        * platform/graphics/GraphicsContext.h:
        * platform/graphics/cg/GraphicsContextCG.cpp:
        (WebCore::GraphicsContext::fillRect):
        (WebCore::GraphicsContext::fillRoundedRect):
        (WebCore::GraphicsContext::fillRectWithRoundedHole):
        (WebCore::GraphicsContext::setIsCALayerContext):
        (WebCore::GraphicsContext::isCALayerContext):
        (WebCore::GraphicsContext::setIsAcceleratedContext):
        (WebCore::GraphicsContext::isAcceleratedContext):
        * platform/graphics/cg/GraphicsContextPlatformPrivateCG.h:
        (WebCore::GraphicsContextPlatformPrivate::GraphicsContextPlatformPrivate):
        * platform/graphics/mac/WebLayer.mm:
        (drawLayerContents):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@81161 268f45cc-cd09-0410-ab3c-d52691b4dbfc