Fix VideoDecoderShim to return correct decode_id for all codecs.

media/base/video_decoder.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_BASE_VIDEO_DECODER_H_
 #define MEDIA_BASE_VIDEO_DECODER_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 60 matching lines @@
   // GetMaxDecodeRequests() to get number of buffers that may be decoded in
   // parallel. Decoder must call |decode_cb| in the same order in which Decode()
   // is called.
   //
   // Implementations guarantee that the callback will not be called from within
   // this method and that |decode_cb| will not be blocked on the following
   // Decode() calls (i.e. |decode_cb| will be called even if Decode() is never
   // called again).
   //
   // After decoding is finished the decoder calls |output_cb| specified in
-  // Initialize() for each decoded frame. |output_cb| may be called before or
-  // after |decode_cb|.
+  // Initialize() for each decoded frame. In general |output_cb| may be called
+  // before or after |decode_cb|, but software decoders must call |output_cb|

[xhwang, 2015/01/22 23:52:43]

I get what you mean, but this can be complicated. For example, the hardware
decoder (GpuVideoDecoder) on Mac can fallback to software mode internally. 

I suggest you do the same as |low_delay| where VideoDecoderShim assumes FFVD and
VPxVD always do this and relax this requirement to a recommendation. But it's up
to you :)

[Sergey Ulanov, 2015/01/23 00:19:37]

Done.

+  // before calling |decode_cb|, i.e. while Decode() is pending.
   //
   // If |buffer| is an EOS buffer then the decoder must be flushed, i.e.
   // |output_cb| must be called for each frame pending in the queue and
   // |decode_cb| must be called after that. Callers will not call Decode()
   // again until after the flush completes.
   virtual void Decode(const scoped_refptr<DecoderBuffer>& buffer,
                       const DecodeCB& decode_cb) = 0;
 
   // Resets decoder state. All pending Decode() requests will be finished or
   // aborted before |closure| is called.
@@ skipping 12 matching lines @@
   // Returns maximum number of parallel decode requests.
   virtual int GetMaxDecodeRequests() const;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(VideoDecoder);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_DECODER_H_