Add observer for AVAudioSession.outputVolume

webrtc/modules/audio_device/ios/objc/RTCAudioSession.h

Index: webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
diff --git a/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h b/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
index 155929cfc7d6fd1735cdb364b3cd8fe9710c36bb..56c10c0bb1f22dacaf8f547b7f165e830d7e34a5 100644
--- a/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
+++ b/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
@@ -74,6 +74,9 @@ RTC_EXPORT
  */
 - (void)audioSessionDidStopPlayOrRecord:(RTCAudioSession *)session;
 
+/** Called when the AVAudioSession output volume value changes. */
+- (void)audioVolumeDidChange:(float)volume;

[tkchin_webrtc, 2017/05/25 20:24:32]

follow delegate naming convention and use the same property name
- (void)audioSession:(RTCAudioSession *)audioSession
didChangeOutputVolume:(float)outputVolume;

+
 @end
 
 /** This is a protocol used to inform RTCAudioSession when the audio session