Right now, RenderWidgetHostImpl receives:
- ViewHostMsg_SwapCompositorFrame
- ViewHostMsg_SetNeedsBeginFrames
- ViewHostMsg_BeginFrameDidNotSwap

but RenderWidgetHostView* sends:
- ViewMsg_BeginFrame
- ViewMsg_SetBeginFramePaused
- ViewMsg_ReclaimCompositorResources

CompositorFrameSinkSupport is owned by:
- DelegatedFrameHost
- DelegatedFrameHostAndroid
- RenderWidgetHostViewChildFrame

Once we mojoify things, we want the MojoCompositorFrameSink to contain CompositorFrameSinkSupport and handle all the said messages.