Reviewed by Dirk Schulze.

        [OpenVG] Use masks to implement non-rectilinear clipping
        https://bugs.webkit.org/show_bug.cgi?id=35544

        Requires some additional context switching logic to
        make sure the right context is current when dealing
        with the mask, because we don't store it by ourselves.

        Initial version of this code was written by
        Eli Fidler <efidler@rim.com>, I did a couple of
        bug fixes and efficiency improvements since then.

        * platform/graphics/openvg/GraphicsContextOpenVG.cpp:
        (WebCore::GraphicsContext::clipPath):
        (WebCore::GraphicsContext::clip):
        (WebCore::GraphicsContext::clipOut):
        (WebCore::GraphicsContext::clipOutEllipseInRect):
        (WebCore::GraphicsContext::addInnerRoundedRectClip):
        * platform/graphics/openvg/PainterOpenVG.cpp:
        (WebCore::PlatformPainterState::PlatformPainterState):
        (WebCore::PlatformPainterState::~PlatformPainterState):
        (WebCore::PlatformPainterState::maskingEnabled):
        (WebCore::PlatformPainterState::applyState):
        (WebCore::PlatformPainterState::saveMaskIfNecessary):
        (WebCore::PainterOpenVG::intersectClipRect):
        (WebCore::PainterOpenVG::clipPath):
        (WebCore::PainterOpenVG::save):
        * platform/graphics/openvg/PainterOpenVG.h:
        (WebCore::PainterOpenVG::):
        * platform/graphics/openvg/SurfaceOpenVG.cpp:
        (WebCore::SurfaceOpenVG::makeCurrent):
        (WebCore::SurfaceOpenVG::makeCompatibleCurrent):
        * platform/graphics/openvg/SurfaceOpenVG.h:
        (WebCore::SurfaceOpenVG::):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@55922 268f45cc-cd09-0410-ab3c-d52691b4dbfc