Support for the Chromium-specific extension GL_CHROMIUM_copy_texture_to_parent_texture is needed in WebKit/chromium/src/WebGraphicsContext3DDefaultImpl.cpp in order for the accelerated 2D canvas to work properly in DumpRenderTree. Currently I suspect that any pixel tests will fail.
Good catch. Just to be clear, it's only with both --enable-accelerated-compositing and --enable-accelerated-2d-canvas that the tests will fail. They should still work with --enable-accelerated-2d-canvas alone.
*** This bug has been marked as a duplicate of bug 48152 ***