Reviewed by Simon Fraser.

        Animated scaling of background-image is too slow
        https://bugs.webkit.org/show_bug.cgi?id=33808

        Implement a version of the RenderImage animated scaling optimisation
        for background images.  Due to the possibility of arbitrary transforms
        being applied to containing elements we explicitly check the current
        CTM of the context for scaling or rotation.

        * platform/graphics/GraphicsContext.cpp:
        (WebCore::GraphicsContext::drawTiledImage):
        * platform/graphics/GraphicsContext.h:
        * platform/graphics/transforms/TransformationMatrix.h:
        (WebCore::TransformationMatrix::isIdentityOrTranslation):
        * rendering/RenderBoxModelObject.cpp:
        (WebCore::RenderBoxModelScaleData::RenderBoxModelScaleData):
        (WebCore::RenderBoxModelScaleData::~RenderBoxModelScaleData):
        (WebCore::RenderBoxModelScaleData::size):
        (WebCore::RenderBoxModelScaleData::time):
        (WebCore::RenderBoxModelScaleData::useLowQualityScale):
        (WebCore::RenderBoxModelScaleData::hiqhQualityRepaintTimer):
        (WebCore::RenderBoxModelScaleData::setSize):
        (WebCore::RenderBoxModelScaleData::setTime):
        (WebCore::RenderBoxModelScaleData::setUseLowQualityScale):
        (WebCore::RenderBoxModelScaleObserver::boxModelObjectDestroyed):
        (WebCore::RenderBoxModelScaleObserver::highQualityRepaintTimerFired):
        (WebCore::RenderBoxModelScaleObserver::shouldPaintBackgroundAtLowQuality):
        (WebCore::RenderBoxModelObject::highQualityRepaintTimerFired):
        (WebCore::RenderBoxModelObject::~RenderBoxModelObject):
        (WebCore::RenderBoxModelObject::paintFillLayerExtended):
        * rendering/RenderBoxModelObject.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@53949 268f45cc-cd09-0410-ab3c-d52691b4dbfc