Introduce AudioDecoderConfig to migrate away from GetAVStream().

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index ed59c877f4329e5e62d0bffdd47bdb9dcb983346..e9bd12729c2e4c6affbf886a873197219625d3ef 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -28,6 +28,7 @@
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/synchronization/waitable_event.h"
+#include "media/base/audio_decoder_config.h"
 #include "media/base/buffers.h"
 #include "media/base/demuxer.h"
 #include "media/base/pipeline.h"
@@ -55,22 +56,22 @@ class FFmpegDemuxerStream : public DemuxerStream {
   // Returns true is this stream has pending reads, false otherwise.
   //
   // Safe to call on any thread.
-  virtual bool HasPendingReads();
+  bool HasPendingReads();
 
   // Enqueues and takes ownership over the given AVPacket.
-  virtual void EnqueuePacket(AVPacket* packet);
+  void EnqueuePacket(AVPacket* packet);
 
   // Signals to empty the buffer queue and mark next packet as discontinuous.
-  virtual void FlushBuffers();
+  void FlushBuffers();
 
   // Empties the queues and ignores any additional calls to Read().
-  virtual void Stop();
+  void Stop();
 
   // Returns the duration of this stream.
-  virtual base::TimeDelta duration();
+  base::TimeDelta duration();
 
   // DemuxerStream implementation.
-  virtual Type type();
+  virtual Type type() OVERRIDE;
 
   // If |buffer_queue_| is not empty will execute on caller's thread, otherwise
   // will post ReadTask to execute on demuxer's thread. Read will acquire
@@ -78,10 +79,10 @@ class FFmpegDemuxerStream : public DemuxerStream {
   // not make calls into FFmpegDemuxerStream directly or that may cause a
   // deadlock. |read_callback| should execute as quickly as possible because
   // |lock_| is held throughout the life of the callback.
-  virtual void Read(const ReadCallback& read_callback);
-  // Bitstream converter to convert input packet.
-  virtual void EnableBitstreamConverter();
-  virtual AVStream* GetAVStream();
+  virtual void Read(const ReadCallback& read_callback) OVERRIDE;
+  virtual void EnableBitstreamConverter() OVERRIDE;
+  virtual AVStream* GetAVStream() OVERRIDE;
+  virtual const AudioDecoderConfig& audio_decoder_config() OVERRIDE;
 
  private:
   virtual ~FFmpegDemuxerStream();
@@ -100,6 +101,7 @@ class FFmpegDemuxerStream : public DemuxerStream {
 
   FFmpegDemuxer* demuxer_;
   AVStream* stream_;
+  AudioDecoderConfig audio_config_;
   Type type_;
   base::TimeDelta duration_;
   bool discontinuous_;