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

media/cast/test/utility/audio_utility.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <math.h>
 
 #include "media/cast/test/utility/audio_utility.h"
 
 #include "base/time/time.h"
 #include "media/base/audio_bus.h"
@@ skipping 35 matching lines @@
   scoped_ptr<PcmAudioFrame> audio_frame(new PcmAudioFrame());
   audio_frame->channels = audio_bus.channels();
   audio_frame->frequency = sample_rate;
   audio_frame->samples.resize(audio_bus.channels() * audio_bus.frames());
   audio_bus.ToInterleaved(audio_bus.frames(),
                           sizeof(audio_frame->samples.front()),
                           &audio_frame->samples.front());
   return audio_frame.Pass();
 }
 
+int CountZeroCrossings(const float* samples, int len) {
+  // The sample values must pass beyond |kAmplitudeThreshold| on the opposite
+  // side of zero before a crossing will be counted.
+  const float kAmplitudeThreshold = 0.03f;  // 3% of max amplitude.
+
+  int count = 0;
+  int i = 0;
+  float last = 0.0f;
+  for (; i < len && fabsf(last) < kAmplitudeThreshold; ++i)
+    last = samples[i];
+  for (; i < len; ++i) {
+    if (fabsf(samples[i]) >= kAmplitudeThreshold &&
+        (last < 0) != (samples[i] < 0)) {
+      ++count;
+      last = samples[i];
+    }
+  }
+  return count;
+}
+
 int CountZeroCrossings(const std::vector<int16>& samples) {
   // The sample values must pass beyond |kAmplitudeThreshold| on the opposite
   // side of zero before a crossing will be counted.
   const int kAmplitudeThreshold = 1000;  // Approx. 3% of max amplitude.
 
   int count = 0;
   std::vector<int16>::const_iterator i = samples.begin();
   int16 last = 0;
   for (; i != samples.end() && abs(last) < kAmplitudeThreshold; ++i)
     last = *i;
@@ skipping 122 matching lines @@
       }
       *timestamp = gray_coded;
       return true;
     }
   }
   return false;
 }
 
 }  // namespace cast
 }  // namespace media