[Cast] Remove AudioDecoder's dependency on WebRTC, and refactor/clean-up AudioReceiver.

media/cast/audio_receiver/audio_receiver.gypi

Index: media/cast/audio_receiver/audio_receiver.gypi
diff --git a/media/cast/audio_receiver/audio_receiver.gypi b/media/cast/audio_receiver/audio_receiver.gypi
index 16b425cd212fc62bbfcafff8636bc548846537bc..048227cd6419e511eb4055d51941ffecf634750a 100644
--- a/media/cast/audio_receiver/audio_receiver.gypi
+++ b/media/cast/audio_receiver/audio_receiver.gypi
@@ -19,10 +19,12 @@
         'audio_receiver.cc',
       ], # source
       'dependencies': [
+        '<(DEPTH)/media/media.gyp:media',
+        '<(DEPTH)/media/media.gyp:shared_memory_support',
         '<(DEPTH)/media/cast/transport/utility/utility.gyp:transport_utility',
         '<(DEPTH)/media/cast/rtcp/rtcp.gyp:cast_rtcp',
         '<(DEPTH)/media/cast/rtp_receiver/rtp_receiver.gyp:cast_rtp_receiver',
-        '<(DEPTH)/third_party/webrtc/webrtc.gyp:webrtc',
+        '<(DEPTH)/third_party/opus/opus.gyp:opus',
       ],
     },
   ],