Made MixerAudioSource a pure interface.

webrtc/modules/audio_mixer/audio_mixer_defines.h

 /*
  *  Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 26 matching lines @@
 
   // The implementation of GetAudioFrameWithMuted should update
   // audio_frame with new audio every time it's called. Implementing
   // classes are allowed to return the same AudioFrame pointer on
   // different calls. The pointer must stay valid until the next
   // mixing call or until this audio source is disconnected from the
   // mixer.
   virtual AudioFrameWithMuted GetAudioFrameWithMuted(int32_t id,
                                                      int sample_rate_hz) = 0;
 
-  // Returns true if the audio source was mixed this mix iteration.
-  bool IsMixed() const;
-
-  // Returns true if the audio source was mixed previous mix
-  // iteration.
-  bool WasMixed() const;
-
-  // Updates the mixed status.
-  int32_t SetIsMixed(bool mixed);
-
-  void ResetMixedStatus();
-
- private:
-  bool is_mixed_;
-
  protected:
   MixerAudioSource();
   virtual ~MixerAudioSource();

[the sun, 2016/10/04 20:36:09]

- Remove ctor.
- Make the dtor inline and move to top of class declaration (among the methods).

[aleloi, 2016/10/05 15:18:18]

I don't understand what you mean by moving the dtor to the top. Do you want to
make it public? I think a protected virtual destructor helps documenting that
something is a pure virtual base class.

[the sun, 2016/10/05 19:32:10]

A protected virtual destructor means that the object cannot be deleted using a
MixerAudioSource pointer. I don't think it is up to us to decide here how
someone implementing the interface manages objects, so yes, make the dtor public
and virtual.

But thanks for pushing back - the AudioMixer dtor should indeed be protected,
but only once the interface inherits RefCountInterface. The reason of course
being that it should only be deleted from Release().

[aleloi, 2016/10/06 09:26:12]

I see. Good point!

 };
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_MIXER_AUDIO_MIXER_DEFINES_H_