Gracefully handle multiple Flush/Reset/Decode with same id

ppapi/shared_impl/video_decoder_impl.h

 // Copyright (c) 2011 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 PPAPI_SHARED_IMPL_VIDEO_DECODER_IMPL_H_
 #define PPAPI_SHARED_IMPL_VIDEO_DECODER_IMPL_H_
 
 #include <map>
 #include <vector>
 
@@ skipping 26 matching lines @@
 
   // PPB_VideoDecoder_API implementation.
   virtual void Destroy() OVERRIDE;
 
   // Copy C-style config list into |out_configs| vector.
   static bool CopyConfigsToVector(
       const PP_VideoConfigElement* configs_to_copy,
       std::vector<PP_VideoConfigElement>* out_configs);
 
  protected:
-  void SetFlushCallback(PP_CompletionCallback callback);
-  void SetResetCallback(PP_CompletionCallback callback);
-  void SetBitstreamBufferCallback(
+  bool SetFlushCallback(PP_CompletionCallback callback);
+  bool SetResetCallback(PP_CompletionCallback callback);
+  bool SetBitstreamBufferCallback(
       int32 bitstream_buffer_id, PP_CompletionCallback callback);
 
   void RunFlushCallback(int32 result);
   void RunResetCallback(int32 result);
   void RunBitstreamBufferCallback(int32 bitstream_buffer_id, int32 result);
 
   // Tell command buffer to process all commands it has received so far.
   void FlushCommandBuffer();
 
   // Initialize the underlying decoder and return success status.
@@ skipping 24 matching lines @@
   // In the out-of-process case, Context3D's gles2_impl() exists in the plugin
   // process only, so gles2_impl_ is NULL in that case.
   gpu::gles2::GLES2Implementation* gles2_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoDecoderImpl);
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_VIDEO_DECODER_IMPL_H_