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

media/cast/test/utility/audio_utility.h

Index: media/cast/test/utility/audio_utility.h
diff --git a/media/cast/test/utility/audio_utility.h b/media/cast/test/utility/audio_utility.h
index 7cc9b7d74cf59808eec1e5295d7cc58784e1e3ed..1cb0585df0d90a6983af585567e085e04ed84d3c 100644
--- a/media/cast/test/utility/audio_utility.h
+++ b/media/cast/test/utility/audio_utility.h
@@ -56,6 +56,8 @@ scoped_ptr<PcmAudioFrame> ToPcmAudioFrame(const AudioBus& audio_bus,
 // Assuming |samples| contains a single-frequency sine wave (and maybe some
 // low-amplitude noise), count the number of times the sine wave crosses
 // zero.
+int CountZeroCrossings(const float* samples, int len);
+// DEPRECATED:
 int CountZeroCrossings(const std::vector<int16>& samples);
 
 // Encode |timestamp| into the samples pointed to by 'samples' in a way