Implement temporary reference assignment with DisplayCompositor.

services/ui/ws/server_window_compositor_frame_sink_manager.h

Index: services/ui/ws/server_window_compositor_frame_sink_manager.h
diff --git a/services/ui/ws/server_window_compositor_frame_sink_manager.h b/services/ui/ws/server_window_compositor_frame_sink_manager.h
index 8eb887b9521ae725d2bcd5f73cbf1f93a408ae43..3545e0172016ff8d2d7befe62c29a384ebafb908 100644
--- a/services/ui/ws/server_window_compositor_frame_sink_manager.h
+++ b/services/ui/ws/server_window_compositor_frame_sink_manager.h
@@ -17,7 +17,6 @@ namespace ui {
 namespace ws {
 
 class ServerWindow;
-class ServerWindowCompositorFrameSink;
 class ServerWindowCompositorFrameSinkManagerTestApi;
 
 struct CompositorFrameSinkData {
@@ -51,11 +50,14 @@ class ServerWindowCompositorFrameSinkManager {
       cc::mojom::MojoCompositorFrameSinkRequest request,
       cc::mojom::MojoCompositorFrameSinkClientPtr client);
 
+  // Claims this FrameSinkId will embed |surface_id| so it should own the
+  // temporary reference to |surface_id|.
+  void ClaimTemporaryReference(const cc::SurfaceId& surface_id);
+
  private:
   friend class ServerWindowCompositorFrameSinkManagerTestApi;
-  friend class ServerWindowCompositorFrameSink;
 
-  ServerWindow* window_;
+  ServerWindow* const window_;
 
   std::unique_ptr<CompositorFrameSinkData> frame_sink_data_;