Reviewed by David Levin.

        When using the Skia graphics context, the beginTransparencyLayer call
        currently creates a new layer, but does not keep the current
        compositing mode for use when merging the created layer back onto the
        rest of the context. This patch fixes that.
        https://bugs.webkit.org/show_bug.cgi?id=34491

        fast/backgrounds/svg-as-mask.html is affected by this change in Chromium,
        but not fixed. This is the first of a series of patches to fix it.

        * platform/graphics/skia/GraphicsContextSkia.cpp:
        (WebCore::GraphicsContext::beginTransparencyLayer):
        * platform/graphics/skia/PlatformContextSkia.cpp:
        (PlatformContextSkia::beginTransparencyLayer):
        * platform/graphics/skia/PlatformContextSkia.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54257 268f45cc-cd09-0410-ab3c-d52691b4dbfc