Introduce AudioDecoderConfig to migrate away from GetAVStream().

media/filters/ffmpeg_demuxer_unittest.cc

Index: media/filters/ffmpeg_demuxer_unittest.cc
diff --git a/media/filters/ffmpeg_demuxer_unittest.cc b/media/filters/ffmpeg_demuxer_unittest.cc
index e6368494b6be064be67ec255607779a7979d1967..f1fc98fdba76015b37692bc22c145ca3c27fd190 100644
--- a/media/filters/ffmpeg_demuxer_unittest.cc
+++ b/media/filters/ffmpeg_demuxer_unittest.cc
@@ -176,12 +176,23 @@ TEST_F(FFmpegDemuxerTest, Initialize_Successful) {
   ASSERT_TRUE(stream);
   EXPECT_EQ(DemuxerStream::VIDEO, stream->type());
   ASSERT_TRUE(stream->GetAVStream());
+  ASSERT_FALSE(stream->audio_decoder_config());
 
   // Other stream should be audio and support the FFmpegDemuxerStream interface.
   stream = demuxer_->GetStream(DemuxerStream::AUDIO);
   ASSERT_TRUE(stream);
   EXPECT_EQ(DemuxerStream::AUDIO, stream->type());
   ASSERT_TRUE(stream->GetAVStream());
+  ASSERT_TRUE(stream->audio_decoder_config());
+
+  // FFmpegDemuxer's audio streams support AudioDecoderConfig structs.
+  AudioDecoderConfig* config = stream->audio_decoder_config();
+  EXPECT_EQ(kCodecVorbis, config->codec());
+  EXPECT_EQ(16, config->bits_per_channel());
+  EXPECT_EQ(CHANNEL_LAYOUT_STEREO, config->channel_layout());
+  EXPECT_EQ(44100, config->sample_rate());
+  EXPECT_TRUE(config->extra_data());
+  EXPECT_GT(config->extra_data_size(), 0u);
 }
 
 TEST_F(FFmpegDemuxerTest, Read_Audio) {