Mus+Ash: Use standard cc mechanism for surface lifetime.

services/ui/ws/server_window.h

Index: services/ui/ws/server_window.h
diff --git a/services/ui/ws/server_window.h b/services/ui/ws/server_window.h
index 89109599669c5b9afea106a45626ba23695ad291..d6266bb42f443391db31c950e5f3611a5599782f 100644
--- a/services/ui/ws/server_window.h
+++ b/services/ui/ws/server_window.h
@@ -56,6 +56,7 @@ class ServerWindow {
 
   void AddObserver(ServerWindowObserver* observer);
   void RemoveObserver(ServerWindowObserver* observer);
+  bool HasObserver(ServerWindowObserver* observer);
 
   // Creates a new surface of the specified type, replacing the existing.
   void CreateSurface(mojom::SurfaceType surface_type,
@@ -161,9 +162,6 @@ class ServerWindow {
   // visible.
   bool IsDrawn() const;
 
-  // Called when its appropriate to destroy surfaces scheduled for destruction.
-  void DestroySurfacesScheduledForDestruction();
-
   const gfx::Insets& extended_hit_test_region() const {
     return extended_hit_test_region_;
   }