Enable fire-and-forget Destroy of HW video decoder, and misc other improvements.

ppapi/cpp/dev/video_decoder_dev.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_CPP_DEV_VIDEO_DECODER_DEV_H_
 #define PPAPI_CPP_DEV_VIDEO_DECODER_DEV_H_
 
 #include <vector>
 
 #include "ppapi/c/dev/pp_video_dev.h"
@@ skipping 24 matching lines @@
   // PPB_VideoDecoder_Dev implementation.
   int32_t Initialize(const PP_VideoConfigElement* config,
                      const Context3D_Dev& context,
                      CompletionCallback callback);
   void AssignGLESBuffers(const std::vector<PP_GLESBuffer_Dev>& buffers);
   int32_t Decode(const PP_VideoBitstreamBuffer_Dev& bitstream_buffer,
                  CompletionCallback callback);
   void ReusePictureBuffer(int32_t picture_buffer_id);
   int32_t Flush(CompletionCallback callback);
   int32_t Reset(CompletionCallback callback);
-  int32_t Destroy(CompletionCallback callback);
+
+ private:
+  // Disallow copy-construction to ensure Destroy() is called exactly once.
+  VideoDecoder_Dev(const VideoDecoder_Dev&);
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_DEV_VIDEO_DECODER_DEV_H_