Run VDA::Decode on GPU IO thread if VDA supports it.

media/video/video_decode_accelerator.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 MEDIA_VIDEO_VIDEO_DECODE_ACCELERATOR_H_
 #define MEDIA_VIDEO_VIDEO_DECODE_ACCELERATOR_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 74 matching lines @@
 
   // Initializes the video decoder with specific configuration.
   // Parameters:
   //  |profile| is the video stream's format profile.
   //
   // Returns true when command successfully accepted. Otherwise false.
   virtual bool Initialize(VideoCodecProfile profile) = 0;
 
   // Decodes given bitstream buffer. Once decoder is done with processing
   // |bitstream_buffer| it will call NotifyEndOfBitstreamBuffer() with the
-  // bitstream buffer id.
+  // bitstream buffer id. In GPU process, this runs on IO thread.

[Ami GONE FROM CHROMIUM, 2013/08/22 14:52:03]

This is a strange comment considering processes & threads are not mentioned
otherwise in this file.  I'd just drop it.

   // Parameters:
   //  |bitstream_buffer| is the input bitstream that is sent for decoding.
   virtual void Decode(const BitstreamBuffer& bitstream_buffer) = 0;
 
   // Assigns a set of texture-backed picture buffers to the video decoder.
   //
   // Ownership of each picture buffer remains with the client, but the client
   // is not allowed to deallocate the buffer before the DismissPictureBuffer
   // callback has been initiated for a given buffer.
   //
@@ skipping 25 matching lines @@
   // component is freed.  This call may asynchornously free system resources,
   // but its client-visible effects are synchronous.  After this method returns
   // no more callbacks will be made on the client.  Deletes |this|
   // unconditionally, so make sure to drop all pointers to it!
   virtual void Destroy() = 0;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_VIDEO_VIDEO_DECODE_ACCELERATOR_H_