Reviewed by David Levin.

        [CHROMIUM] Use the BGRA format for canvas 2D accel upload and readbacks.
        https://bugs.webkit.org/show_bug.cgi?id=43804

        Use the BGRA format from GraphicsContext3D, if supported.  Also keep a
        texture around for uploads, rather than re-creating it each time.

        Covered by many layout tests (once we're running them).

        * platform/graphics/chromium/GLES2Texture.cpp:
        (WebCore::convertFormat):
        Move convertFormat() ahead of texture creation, so we can check for
        BGRA support.
        (WebCore::GLES2Texture::create):
        Use convertFormat() to determine the correct format and types to use;
        use the returned format also for internalFormat, since GLES2 insists
        they match.
        * platform/graphics/skia/PlatformContextSkia.cpp:
        (WebCore::PlatformContextSkia::setGraphicsContext3D):
        Clear the upload texture when a new context is set.
        (WebCore::PlatformContextSkia::uploadSoftwareToHardware):
        Use m_uploadTexture instead of creating a new one each time.
        (WebCore::PlatformContextSkia::readbackHardwareToSoftware):
        When the context supports it, use the BGRA format for readbacks
        instead of swizzling.
        * platform/graphics/skia/PlatformContextSkia.h:
        Add m_uploadTexture for consecutive uploads.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@65323 268f45cc-cd09-0410-ab3c-d52691b4dbfc