Return resources immediately after a Surface is destroyed

cc/surfaces/surface_observer.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_SURFACES_SURFACE_OBSERVER_H_
 #define CC_SURFACES_SURFACE_OBSERVER_H_
 
 namespace cc {
 
 class SurfaceInfo;
 
 class SurfaceObserver {
  public:
   // Runs when a CompositorFrame is received for the given SurfaceInfo for the
   // first time.
   virtual void OnSurfaceCreated(const SurfaceInfo& surface_info) = 0;
 
   // Runs when a Surface is damaged. *changed should be set to true if this
   // causes a Display to be damaged.
   virtual void OnSurfaceDamaged(const SurfaceId& surface_id, bool* changed) = 0;
+
+  // Called when a surface is garbage-collected.
+  virtual void OnSurfaceDiscarded(const SurfaceId& surface_id) = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_OBSERVER_H_