Implement temporary reference assignment with DisplayCompositor.

services/ui/ws/window_server.h

Index: services/ui/ws/window_server.h
diff --git a/services/ui/ws/window_server.h b/services/ui/ws/window_server.h
index 97be57b3bbd8b1db0280a073dfcfd4604c53e7ed..c117dae451bddd3e6556a6b593d57281cab3d3cf 100644
--- a/services/ui/ws/window_server.h
+++ b/services/ui/ws/window_server.h
@@ -283,6 +283,13 @@ class WindowServer : public ServerWindowDelegate,
 
   bool IsUserInHighContrastMode(const UserId& user) const;
 
+  // Finds the parent client that will embed |surface_id| and claims ownership
+  // of the temporary reference. If no parent client is found then tell GPU to
+  // immediately drop the temporary reference. |window| is the ServerWindow
+  // that corresponds to |surface_id|.
+  void ClaimTemporaryReference(ServerWindow* window,
+                               const cc::SurfaceId& surface_id);
+
   // Overridden from ServerWindowDelegate:
   ServerWindow* GetRootWindow(const ServerWindow* window) override;