Reviewed by Alexey Proskuryakov.

        Cache CGColor as we do NSColor
        https://bugs.webkit.org/show_bug.cgi?id=47226

        This fixes performance problems on certain web pages that use
        multiple colors. Once in the past we were using NSColor. Now that
        we are using CGColor, we need the same sort of caching that we have
        for NSColor.

        One example: <http://results.active.com/uploads/html/100759.html>.

        * WebCore.xcodeproj/project.pbxproj: Add GraphicsContextCG.h.

        * platform/graphics/Color.h: Replace createCGColor with cachedCGColor.

        * platform/graphics/cg/ColorCG.cpp:
        (WebCore::cachedCGColorSpace): Added.
        (WebCore::leakCGColor): Added. 
        (WebCore::cachedCGColor): Added.

        * platform/graphics/cg/GraphicsContextCG.cpp:
        (WebCore::setCGFillColor): Use cachedCGColor.
        (WebCore::setCGStrokeColor): Ditto.
        (WebCore::GraphicsContext::fillRect): Ditto.
        (WebCore::GraphicsContext::setPlatformShadow): Ditto.

        * platform/graphics/cg/GraphicsContextCG.h: Added.
        * platform/graphics/cg/GraphicsContextPlatformPrivateCG.h:
        Moved the color space functions here.

        * platform/graphics/cg/ImageCG.cpp: Tweaked headers and formatting.

        * platform/graphics/mac/ColorMac.mm: Removed the createCGColor
        function.

        * platform/graphics/mac/GraphicsContextMac.mm:
        (WebCore::drawFocusRingToContext): Removed innappropriate use of
        RetainPtr for the arguments to this function.
        (WebCore::GraphicsContext::drawFocusRing): Use cachedCGColor.

        * platform/graphics/mac/GraphicsLayerCA.mm:
        (WebCore::setLayerBorderColor): Use cachedCGColor.
        (WebCore::setLayerBackgroundColor): Ditto.
        * platform/graphics/win/GraphicsContextCGWin.cpp:
        (WebCore::GraphicsContext::drawFocusRing): Ditto.
        * platform/graphics/win/GraphicsLayerCACF.cpp:
        (WebCore::setLayerBorderColor): Ditto.
        (WebCore::setLayerBackgroundColor): Ditto.

        * platform/graphics/win/WKCACFLayerRenderer.cpp:
        (WebCore::WKCACFLayerRenderer::WKCACFLayerRenderer): Use
        CGColorCreateGenericRGB for color used only for debugging.
        * platform/graphics/win/WebTiledLayer.cpp:
        (WebCore::WebTiledLayer::addTile): Ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@69259 268f45cc-cd09-0410-ab3c-d52691b4dbfc