implement getBufferSubDataAsync prototype

gpu/command_buffer/client/gles2_interface.h

 // Copyright (c) 2012 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 GPU_COMMAND_BUFFER_CLIENT_GLES2_INTERFACE_H_
 #define GPU_COMMAND_BUFFER_CLIENT_GLES2_INTERFACE_H_
 
 #include <GLES2/gl2.h>
 
 #include "base/compiler_specific.h"
 
 extern "C" typedef struct _ClientBuffer* ClientBuffer;
 
 namespace gpu {
 namespace gles2 {
 
 // This class is the interface for all client side GL functions.
 class GLES2Interface {
  public:
   GLES2Interface() {}
   virtual ~GLES2Interface() {}
 
+  virtual void FreeSharedMemory(void*) {};
+
   // Include the auto-generated part of this class. We split this because
   // it means we can easily edit the non-auto generated parts right here in
   // this file instead of having to edit some template or the code generator.
   #include "gpu/command_buffer/client/gles2_interface_autogen.h"
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_GLES2_INTERFACE_H_