[Chromoting] Implement down mixing in AudioPump

remoting/protocol/audio_pump.h

 // Copyright 2016 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 REMOTING_PROTOCOL_AUDIO_PUMP_H_
 #define REMOTING_PROTOCOL_AUDIO_PUMP_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 11 matching lines @@
 class AudioEncoder;
 class AudioPacket;
 
 namespace protocol {
 
 class AudioStub;
 class AudioSource;
 
 // AudioPump is responsible for fetching audio data from the AudioCapturer
 // and encoding it before passing it to the AudioStub for delivery to the
-// client. Audio is captured and encoded on the audio thread and then passed to
-// AudioStub on the network thread.
+// client. Audio data will be downmixed to stereo if needed. Audio is captured
+// and encoded on the audio thread and then passed to AudioStub on the network
+// thread.
 class AudioPump : public AudioStream {
  public:
   // The caller must ensure that the |audio_stub| is not destroyed until the
   // pump is destroyed.
   AudioPump(scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner,
             std::unique_ptr<AudioSource> audio_source,
             std::unique_ptr<AudioEncoder> audio_encoder,
             AudioStub* audio_stub);
   ~AudioPump() override;
 
@@ skipping 18 matching lines @@
 
   base::WeakPtrFactory<AudioPump> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioPump);
 };
 
 }  // namespace protocol
 }  // namespace remoting
 
 #endif  // REMOTING_PROTOCOL_AUDIO_PUMP_H_