Reland of https://codereview.webrtc.org/2396483002/

webrtc/modules/audio_mixer/audio_mixer_defines.h

Index: webrtc/modules/audio_mixer/audio_mixer_defines.h
diff --git a/webrtc/modules/audio_mixer/audio_mixer_defines.h b/webrtc/modules/audio_mixer/audio_mixer_defines.h
index 57e7f5027e4bf338843d8e1a3a0a0b48fbd7ef96..970a01de02e10663f656aad767fa0d1c74d91911 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_defines.h
+++ b/webrtc/modules/audio_mixer/audio_mixer_defines.h
@@ -35,6 +35,8 @@ class MixerAudioSource {
     AudioFrameInfo audio_frame_info;
   };
 
+  virtual ~MixerAudioSource() = default;
+
   // 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
@@ -43,25 +45,6 @@ class MixerAudioSource {
   // 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();
 };
 }  // namespace webrtc