Add AudioReceiveStream::SetGain() method and use that in WVoMC::SetOutputVolume().

webrtc/audio_receive_stream.h

Index: webrtc/audio_receive_stream.h
diff --git a/webrtc/audio_receive_stream.h b/webrtc/audio_receive_stream.h
index 9af84a71fa042039bfd232a5cad26765631e0ca0..05d456b2b042ed98d8924dcf75b48fc91350f988 100644
--- a/webrtc/audio_receive_stream.h
+++ b/webrtc/audio_receive_stream.h
@@ -124,6 +124,10 @@ class AudioReceiveStream {
   // of feeding to the AEC.
   virtual void SetSink(std::unique_ptr<AudioSinkInterface> sink) = 0;
 
+  // Sets playback gain of the stream, applied when mixing, and thus after it
+  // is potentially forwarded to any attached AudioSinkInterface implementation.

[kwiberg-webrtc, 2016/06/16 09:26:53]

What gain is in effect prior to this method being called? And what unit or
similar does the gain number have?

[the sun, 2016/06/16 14:34:06]

A gain is simply a factor to multiply with. It doesn't have a unit. Nominal gain
is usually (and in this specific case) 1.0.

[kwiberg-webrtc, 2016/06/17 07:38:54]

OK. If this is well known to everyone except me, I guess it doesn't need a
comment.

[the sun, 2016/06/17 08:50:23]

Gain is a very common concept in audio engineering.

+  virtual void SetGain(float gain) = 0;
+
  protected:
   virtual ~AudioReceiveStream() {}
 };