Limit outstanding surface draw swaps to max_frames_pending.

cc/surfaces/display_client.h

 // Copyright 2014 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_DISPLAY_CLIENT_H_
 #define CC_SURFACES_DISPLAY_CLIENT_H_
 
 #include "base/memory/scoped_ptr.h"
 
 namespace cc {
 
 class OutputSurface;
 
 class DisplayClient {
  public:
   virtual scoped_ptr<OutputSurface> CreateOutputSurface() = 0;
   virtual void DisplayDamaged() = 0;
+  virtual void DidSwapBuffers() = 0;
+  virtual void DidSwapBuffersComplete() = 0;
 
  protected:
   virtual ~DisplayClient() {}
 };
 }
 
 #endif  // CC_SURFACES_DISPLAY_CLIENT_H_