Move FrameSink hierarchy registration to DisplayCompositor interface

cc/ipc/display_compositor.mojom

Index: cc/ipc/display_compositor.mojom
diff --git a/cc/ipc/display_compositor.mojom b/cc/ipc/display_compositor.mojom
index 52b688aafd62cd930c54aa99de03ad63e015d645..5e4813f067553ce9e2f803c863c07d9b863996fe 100644
--- a/cc/ipc/display_compositor.mojom
+++ b/cc/ipc/display_compositor.mojom
@@ -57,6 +57,16 @@ interface DisplayCompositor {
       cc.mojom.MojoCompositorFrameSink& compositor_frame_sink,
       cc.mojom.MojoCompositorFrameSinkPrivate& compositor_frame_sink_private,
       cc.mojom.MojoCompositorFrameSinkClient compositor_frame_sink_client);
+
+  // Set up a BeginFrame relationship between two FrameSinkIds. In this case,
+  // the child inherits the BeginFrameSource from the parent if it doesn't
+  // already have a BeginFrameSource.
+  RegisterFrameSinkHierarchy(cc.mojom.FrameSinkId parent_frame_sink_id,
+                             cc.mojom.FrameSinkId child_frame_sink_id);
+
+  // Removes a BeginFrame relationship between two FrameSinkIds.
+  UnregisterFrameSinkHierarchy(cc.mojom.FrameSinkId parent_frame_sink_id,
+                               cc.mojom.FrameSinkId child_frame_sink_id);
 };
 
 // The DisplayCompositorClient interface is implemented by the Display