AnalyserNode should downmix channels to mono.

third_party/WebKit/Source/modules/webaudio/RealtimeAnalyser.h

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 59 matching lines @@
     static const unsigned DefaultFFTSize;
     static const unsigned MinFFTSize;
     static const unsigned MaxFFTSize;
     static const unsigned InputBufferSize;
 
 private:
     // The audio thread writes the input audio here.
     AudioFloatArray m_inputBuffer;
     unsigned m_writeIndex;
 
+    // Input audio is downmixed to this bus before copying to m_inputBuffer.
+    RefPtr<AudioBus> m_downMixBus;
+
     size_t m_fftSize;
     OwnPtr<FFTFrame> m_analysisFrame;
     void doFFTAnalysis();
 
     // Convert the contents of magnitudeBuffer to byte values, saving the result in |destination|.
     void convertToByteData(DOMUint8Array* destination);
 
     // Convert magnidue buffer to dB, saving the result in |destination|
     void convertFloatToDb(DOMFloat32Array* destination);
 
     // doFFTAnalysis() stores the floating-point magnitude analysis data here.
     AudioFloatArray m_magnitudeBuffer;
     AudioFloatArray& magnitudeBuffer() { return m_magnitudeBuffer; }
 
     // A value between 0 and 1 which averages the previous version of m_magnitudeBuffer with the current analysis magnitude data.
     double m_smoothingTimeConstant;
 
     // The range used when converting when using getByteFrequencyData().
     double m_minDecibels;
     double m_maxDecibels;
 
     // Time at which the FFT was last computed.
     double m_lastAnalysisTime;
 };
 
 } // namespace blink
 
 #endif // RealtimeAnalyser_h