Move FrameSink hierarchy registration to DisplayCompositor interface

cc/surfaces/compositor_frame_sink_support.h

Index: cc/surfaces/compositor_frame_sink_support.h
diff --git a/cc/surfaces/compositor_frame_sink_support.h b/cc/surfaces/compositor_frame_sink_support.h
index 5feef007b7c0405d5b700c23bb48d772979877d3..ac60f6780ebb36dc1d9176e0456f9a44853c2f3a 100644
--- a/cc/surfaces/compositor_frame_sink_support.h
+++ b/cc/surfaces/compositor_frame_sink_support.h
@@ -53,8 +53,6 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   void Require(const LocalSurfaceId& local_surface_id,
                const SurfaceSequence& sequence);
   void Satisfy(const SurfaceSequence& sequence);
-  void AddChildFrameSink(const FrameSinkId& child_frame_sink_id);
-  void RemoveChildFrameSink(const FrameSinkId& child_frame_sink_id);
   void RequestCopyOfSurface(std::unique_ptr<CopyOutputRequest> request);
   void ForceReclaimResources();
 
@@ -116,9 +114,6 @@ class CC_SURFACES_EXPORT CompositorFrameSinkSupport
   // compositor frame sink.
   ReferencedSurfaceTracker reference_tracker_;
 
-  // The set of BeginFrame children of this CompositorFrameSink.
-  std::unordered_set<FrameSinkId, FrameSinkIdHash> child_frame_sinks_;
-
   const bool is_root_;
 
   // TODO(staraz): Remove this flag once ui::Compositor no longer needs to call