Create a new cross-platform Gradient abstraction and make CanvasGradient wrap it.  This first
        step just cleans up CanvasGradient.  The code that calls it remains ifdef'd however.

        Reviewed by olliej

        * WebCore.pro:
        * WebCore.vcproj/WebCore.vcproj:
        * WebCore.xcodeproj/project.pbxproj:
        * WebCoreSources.bkl:
        * bindings/js/JSCanvasRenderingContext2DCustom.cpp:
        (WebCore::toJS):
        * html/CanvasGradient.cpp:
        (WebCore::CanvasGradient::CanvasGradient):
        * html/CanvasGradient.h:
        (WebCore::CanvasGradient::gradient):
        (WebCore::CanvasGradient::addColorStop):
        (WebCore::CanvasGradient::getColor):
        * html/CanvasRenderingContext2D.cpp:
        (WebCore::CanvasRenderingContext2D::fill):
        (WebCore::CanvasRenderingContext2D::stroke):
        (WebCore::CanvasRenderingContext2D::fillRect):
        * html/CanvasStyle.h:
        (WebCore::CanvasStyle::canvasGradient):
        * platform/graphics/Gradient.cpp: Added.
        (WebCore::Gradient::Gradient):
        (WebCore::Gradient::~Gradient):
        (WebCore::Gradient::addColorStop):
        (WebCore::compareStops):
        (WebCore::Gradient::getColor):
        (WebCore::Gradient::findStop):
        * platform/graphics/Gradient.h: Added.
        (WebCore::Gradient::ColorStop::ColorStop):
        (WebCore::Gradient::platformInit):
        * platform/graphics/cairo/GradientCairo.cpp: Added.
        (WebCore::Gradient::platformDestroy):
        (WebCore::Gradient::platformGradient):
        * platform/graphics/cg/GradientCG.cpp: Added.
        (WebCore::Gradient::platformDestroy):
        (WebCore::gradientCallback):
        (WebCore::Gradient::platformGradient):
        * platform/graphics/qt/GradientQt.cpp: Added.
        (WebCore::Gradient::platformDestroy):
        (WebCore::Gradient::platformGradient):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@31607 268f45cc-cd09-0410-ab3c-d52691b4dbfc