cc: Get rid of SurfaceDestroyed and use SurfaceDiscarded instead

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 {
 
 struct BeginFrameAck;
 struct BeginFrameArgs;
 class SurfaceId;
 class SurfaceInfo;
 
 class SurfaceObserver {
  public:
   // Runs when a CompositorFrame is activated for the given SurfaceInfo for the
   // first time.
   virtual void OnSurfaceCreated(const SurfaceInfo& surface_info) = 0;
 
-  // Runs when a Surface was marked to be destroyed.
-  virtual void OnSurfaceDestroyed(const SurfaceId& surface_id) = 0;
-
   // Runs when a Surface is modified, e.g. when a CompositorFrame is
   // activated, its producer confirms that no CompositorFrame will be submitted
   // in response to a BeginFrame, or a CopyOutputRequest is issued.
   //
   // |ack.sequence_number| is only valid if called in response to a BeginFrame.
   // |*changed| should be set to true if this causes a Display to be damaged.
   virtual void OnSurfaceDamaged(const SurfaceId& surface_id,
                                 const BeginFrameAck& ack,
                                 bool* changed) = 0;
 
   // Called when a surface is garbage-collected.
   virtual void OnSurfaceDiscarded(const SurfaceId& surface_id) = 0;
 
   // Runs when a Surface's CompositorFrame producer has received a BeginFrame
   // and, thus, is expected to produce damage soon.
   virtual void OnSurfaceDamageExpected(const SurfaceId& surface_id,
                                        const BeginFrameArgs& args) = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_OBSERVER_H_