When we discard a surface, we call Display::SurfaceDiscarded which, in turn calls SurfaceAggregator::ReturnResources(surface_id) which tries to return resources to the child. The CompositorFrameSinkSupport is likely being destroyed at that point, and so it might've already lost its connection and cannot return resources. Is this a bug?

We only drop a CompositorFrameSinkSupport on gpu restart right? In that case, does the renderer already through away all resource bookkeeping?