Implement AudioOutputProxy.

media/audio/audio_parameters.h

 // Copyright (c) 2010 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.
 
 #ifndef MEDIA_AUDIO_AUDIO_PARAMETERS_H_
 #define MEDIA_AUDIO_AUDIO_PARAMETERS_H_
 
 #include "base/basictypes.h"
 
 struct AudioParameters {
+  // Compare is useful when AudioParameters is used as a key in std::map.
+  class Compare {
+   public:
+    bool operator()(const AudioParameters& a, const AudioParameters& b) const;
+  };
+
   enum Format {
     AUDIO_PCM_LINEAR = 0,     // PCM is 'raw' amplitude samples.
     AUDIO_PCM_LOW_LATENCY,    // Linear PCM, low latency requested.
     AUDIO_MOCK,               // Creates a dummy AudioOutputStream object.
     AUDIO_LAST_FORMAT         // Only used for validation of format.
   };
 
   // Telephone quality sample rate, mostly for speech-only audio.
   static const uint32 kTelephoneSampleRate = 8000;
   // CD sampling rate is 44.1 KHz or conveniently 2x2x3x3x5x5x7x7.
@@ skipping 14 matching lines @@
   int GetPacketSize() const;
 
   Format format;           // Format of the stream.
   int channels;            // Number of channels.
   int sample_rate;         // Sampling frequency/rate.
   int bits_per_sample;     // Number of bits per sample.
   int samples_per_packet;  // Size of a packet in frames.
 };
 
 #endif  // MEDIA_AUDIO_AUDIO_PARAMETERS_H_