Move media::AudioCodec to its own source file

media/base/audio_decoder_config.cc

Index: media/base/audio_decoder_config.cc
diff --git a/media/base/audio_decoder_config.cc b/media/base/audio_decoder_config.cc
index 9d3f67209ba9d189065d3e63027ceea8a59d00a6..bc9403820b224fa54b5d27ecf147c46b403a8293 100644
--- a/media/base/audio_decoder_config.cc
+++ b/media/base/audio_decoder_config.cc
@@ -9,46 +9,6 @@
 
 namespace media {
 
-// These names come from src/third_party/ffmpeg/libavcodec/codec_desc.c
-std::string GetCodecName(AudioCodec codec) {
-  switch (codec) {
-    case kUnknownAudioCodec:
-      return "unknown";
-    case kCodecAAC:
-      return "aac";
-    case kCodecMP3:
-      return "mp3";
-    case kCodecPCM:
-    case kCodecPCM_S16BE:
-    case kCodecPCM_S24BE:
-      return "pcm";
-    case kCodecVorbis:
-      return "vorbis";
-    case kCodecFLAC:
-      return "flac";
-    case kCodecAMR_NB:
-      return "amr_nb";
-    case kCodecAMR_WB:
-      return "amr_wb";
-    case kCodecPCM_MULAW:
-      return "pcm_mulaw";
-    case kCodecGSM_MS:
-      return "gsm_ms";
-    case kCodecOpus:
-      return "opus";
-    case kCodecPCM_ALAW:
-      return "pcm_alaw";
-    case kCodecEAC3:
-      return "eac3";
-    case kCodecALAC:
-      return "alac";
-    case kCodecAC3:
-      return "ac3";
-  }
-  NOTREACHED();
-  return "";
-}
-
 AudioDecoderConfig::AudioDecoderConfig()
     : codec_(kUnknownAudioCodec),
       sample_format_(kUnknownSampleFormat),