Similar to the work done on RenderFrameProxy, BrowserPlugin will need to begin sending its FrameSinkId information in the --mus path.

Additionally BrowserPlugin::WasResized should only send its data if there is a valid FrameSinkId set.

The caveat to this being that the following must occur, even with no valid FrameSinkId, as it is required to begin the embedding process:

if (delegate_ && size_changed)
    delegate_->DidResizeElement(frame_rect().size());