Move FrameSink hierarchy registration to DisplayCompositor interface

services/ui/ws/window_server.cc

Index: services/ui/ws/window_server.cc
diff --git a/services/ui/ws/window_server.cc b/services/ui/ws/window_server.cc
index 6ca22491bff3e8bf6f985344f2a000304df293ae..3b0446dea15217be18930c59287a6f6f4925ca74 100644
--- a/services/ui/ws/window_server.cc
+++ b/services/ui/ws/window_server.cc
@@ -638,6 +638,15 @@ void WindowServer::OnWindowHierarchyChanged(ServerWindow* window,
 
   ProcessWindowHierarchyChanged(window, new_parent, old_parent);
 
+  if (old_parent) {
+    display_compositor_->UnregisterFrameSinkHierarchy(
+        old_parent->frame_sink_id(), window->frame_sink_id());
+  }
+  if (new_parent) {
+    display_compositor_->RegisterFrameSinkHierarchy(new_parent->frame_sink_id(),
+                                                    window->frame_sink_id());
+  }
+
   UpdateNativeCursorFromMouseLocation(window);
 }