Add Opus decode wrapper to media.

media/base/audio_decoder_config.h

Index: media/base/audio_decoder_config.h
diff --git a/media/base/audio_decoder_config.h b/media/base/audio_decoder_config.h
index ce62eb85a1f6389d3fdac77866eeba19200e1279..76d40b43d5beb062195a13dabe563b8444f1a688 100644
--- a/media/base/audio_decoder_config.h
+++ b/media/base/audio_decoder_config.h
@@ -30,12 +30,14 @@ enum AudioCodec {
   kCodecGSM_MS,
   kCodecPCM_S16BE,
   kCodecPCM_S24BE,
+  // Additional codecs for all platforms.
+  kCodecOpus,
   // DO NOT ADD RANDOM AUDIO CODECS!
   //
   // The only acceptable time to add a new codec is if there is production code
   // that uses said codec in the same CL.
 
-  kAudioCodecMax = kCodecPCM_S24BE  // Must equal the last "real" codec above.
+  kAudioCodecMax = kCodecOpus  // Must equal the last "real" codec above.
 };
 
 // TODO(dalecurtis): FFmpeg API uses |bytes_per_channel| instead of