Reviewed by Alp Toker.

        https://bugs.webkit.org/show_bug.cgi?id=21883
        [CAIRO] globalAlpha has to be stored and restored

        Cairo's globalAlpha has to be stored and reloaded on calling
        save() and restore(). We use the power of GraphicsContextState for this.

        * platform/graphics/GraphicsContextPrivate.h:
        (WebCore::GraphicsContextState::GraphicsContextState):
        * platform/graphics/cairo/GraphicsContextCairo.cpp:
        (WebCore::GraphicsContext::fillPath):
        (WebCore::GraphicsContext::strokePath):
        (WebCore::GraphicsContext::setAlpha):
        (WebCore::GraphicsContext::getAlpha):
        * platform/graphics/cairo/GraphicsContextPlatformPrivateCairo.h:
        (WebCore::GraphicsContextPlatformPrivate::GraphicsContextPlatformPrivate):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@38001 268f45cc-cd09-0410-ab3c-d52691b4dbfc