Cast:Adding cast_transport_config and cleaning up

media/cast/audio_receiver/audio_decoder.cc

Index: media/cast/audio_receiver/audio_decoder.cc
diff --git a/media/cast/audio_receiver/audio_decoder.cc b/media/cast/audio_receiver/audio_decoder.cc
index a761a5a84deb275048f014e3fd735b13a33b5ffd..b817836480fe49c42a6a3fee6b3b5052f01ea932 100644
--- a/media/cast/audio_receiver/audio_decoder.cc
+++ b/media/cast/audio_receiver/audio_decoder.cc
@@ -25,7 +25,7 @@ AudioDecoder::AudioDecoder(scoped_refptr<CastEnvironment> cast_environment,
 
   webrtc::CodecInst receive_codec;
   switch (audio_config.codec) {
-    case kPcm16:
+    case transport::kPcm16:
       receive_codec.pltype = audio_config.rtp_payload_type;
       strncpy(receive_codec.plname, "L16", 4);
       receive_codec.plfreq = audio_config.frequency;
@@ -33,7 +33,7 @@ AudioDecoder::AudioDecoder(scoped_refptr<CastEnvironment> cast_environment,
       receive_codec.channels = audio_config.channels;
       receive_codec.rate = -1;
       break;
-    case kOpus:
+    case transport::kOpus:
       receive_codec.pltype = audio_config.rtp_payload_type;
       strncpy(receive_codec.plname, "opus", 5);
       receive_codec.plfreq = audio_config.frequency;
@@ -41,7 +41,7 @@ AudioDecoder::AudioDecoder(scoped_refptr<CastEnvironment> cast_environment,
       receive_codec.channels = audio_config.channels;
       receive_codec.rate = -1;
       break;
-    case kExternalAudio:
+    case transport::kExternalAudio:
       NOTREACHED() << "Codec must be specified for audio decoder";
       break;
   }