Move media::AudioCodec to its own source file

media/filters/ffmpeg_audio_decoder.cc

Index: media/filters/ffmpeg_audio_decoder.cc
diff --git a/media/filters/ffmpeg_audio_decoder.cc b/media/filters/ffmpeg_audio_decoder.cc
index 8159604a55495f5c947d41be69ba7abc6a40b9c2..a4a9a3dcb36e906c2f95f95921f85c1ad6589d54 100644
--- a/media/filters/ffmpeg_audio_decoder.cc
+++ b/media/filters/ffmpeg_audio_decoder.cc
@@ -128,6 +128,14 @@ static int GetAudioBuffer(struct AVCodecContext* s, AVFrame* frame, int flags) {
   return 0;
 }
 
+// static
+bool FFmpegAudioDecoder::IsCodecSupported(AudioCodec codec,
+                                          SampleFormat sample_format) {
+  FFmpegGlue::InitializeFFmpeg();
+  return avcodec_find_decoder(AudioCodecToCodecID(codec, sample_format)) !=
+         nullptr;
+}
+
 FFmpegAudioDecoder::FFmpegAudioDecoder(
     const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
     const scoped_refptr<MediaLog>& media_log)