Introduce AudioDecoderConfig to migrate away from GetAVStream().

media/base/video_decoder_config.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 MEDIA_BASE_VIDEO_DECODER_CONFIG_H_
 #define MEDIA_BASE_VIDEO_DECODER_CONFIG_H_
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "media/base/media_export.h"
 
 namespace media {
 
 enum VideoCodec {
-  kUnknown,
+  kUnknownVideoCodec,
   kCodecH264,
   kCodecVC1,
   kCodecMPEG2,
   kCodecMPEG4,
   kCodecTheora,
   kCodecVP8,
 
   // DO NOT ADD RANDOM VIDEO CODECS!
   //
   // The only acceptable time to add a new codec is if there is production code
@@ skipping 37 matching lines @@
   // Optional byte data required to initialize video decoders.
   scoped_array<uint8> extra_data_;
   size_t extra_data_size_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(VideoDecoderConfig);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_VIDEO_DECODER_CONFIG_H_