Reviewed by Kenneth Russell.

        [chromium] Always do 2d canvas clearRect() in hardware
        https://bugs.webkit.org/show_bug.cgi?id=45415

        r67003 forced Canvas 2d's clearRect() to happen in software if a gradient/shadow/etc was
        active.  This is subtly wrong for mixed mode rendering since it results in only the
        software backing store being cleared and not the hardware.  This forces clearRect() to
        happen in hardware.  Since we upload mixed mode results before doing any hardware draw
        this means we always clear everything.

        * platform/graphics/skia/GraphicsContextSkia.cpp:
        (WebCore::GraphicsContext::clearRect):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@67039 268f45cc-cd09-0410-ab3c-d52691b4dbfc