Made MixerAudioSource a pure interface.

webrtc/modules/audio_mixer/audio_mixer_defines.cc

Index: webrtc/modules/audio_mixer/audio_mixer_defines.cc
diff --git a/webrtc/modules/audio_mixer/audio_mixer_defines.cc b/webrtc/modules/audio_mixer/audio_mixer_defines.cc
index 7779bedfddde7273419b91bac63a96e6d6ecd0d6..11369a78bf73657e80aac2970a39b655982a4d1c 100644
--- a/webrtc/modules/audio_mixer/audio_mixer_defines.cc
+++ b/webrtc/modules/audio_mixer/audio_mixer_defines.cc
@@ -16,23 +16,5 @@ MixerAudioSource::MixerAudioSource() {}
 
 MixerAudioSource::~MixerAudioSource() {}
 
-bool MixerAudioSource::IsMixed() const {
-  return is_mixed_;
-}
-
-bool MixerAudioSource::WasMixed() const {
-  // Was mixed is the same as is mixed depending on perspective. This function
-  // is for the perspective of AudioMixerImpl.
-  return IsMixed();
-}
-
-int32_t MixerAudioSource::SetIsMixed(const bool mixed) {
-  is_mixed_ = mixed;
-  return 0;
-}
-
-void MixerAudioSource::ResetMixedStatus() {
-  is_mixed_ = false;
-}
 
 }  // namespace webrtc