Introduce AudioDecoderConfig to migrate away from GetAVStream().

media/filters/chunk_demuxer.cc

Index: media/filters/chunk_demuxer.cc
diff --git a/media/filters/chunk_demuxer.cc b/media/filters/chunk_demuxer.cc
index 89efadbbbcd1e2a19febbf6704b55c9cc6582df3..88a7f20769ba6c698ac3293a1f958597238f23fa 100644
--- a/media/filters/chunk_demuxer.cc
+++ b/media/filters/chunk_demuxer.cc
@@ -80,12 +80,14 @@ class ChunkDemuxerStream : public DemuxerStream {
   virtual Type type();
   virtual void EnableBitstreamConverter();
   virtual AVStream* GetAVStream();
+  virtual AudioDecoderConfig* audio_decoder_config();
 
  private:
   static void RunCallback(ReadCallback cb, scoped_refptr<Buffer> buffer);
 
   Type type_;
   AVStream* av_stream_;
+  scoped_ptr<AudioDecoderConfig> audio_config_;
 
   mutable base::Lock lock_;
   ReadCBQueue read_cbs_;
@@ -107,6 +109,9 @@ ChunkDemuxerStream::ChunkDemuxerStream(Type type, AVStream* stream)
       shutdown_called_(false),
       received_end_of_stream_(false),
       last_buffer_timestamp_(kNoTimestamp) {
+  if (type_ == AUDIO) {
+    audio_config_.reset(AVCodecContextToAudioDecoderConfig(stream->codec));
+  }
 }
 
 ChunkDemuxerStream::~ChunkDemuxerStream() {}
@@ -281,6 +286,10 @@ void ChunkDemuxerStream::EnableBitstreamConverter() {}
 
 AVStream* ChunkDemuxerStream::GetAVStream() { return av_stream_; }
 
+AudioDecoderConfig* ChunkDemuxerStream::audio_decoder_config() {
+  return audio_config_.get();
+}
+
 ChunkDemuxer::ChunkDemuxer(ChunkDemuxerClient* client)
     : state_(WAITING_FOR_INIT),
       client_(client),