Add PeerConnectionObserver::OnRemoveTrack callback.

webrtc/api/peerconnectioninterface.h

 /*
  *  Copyright 2012 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 843 matching lines @@
   // Called when the ICE connection receiving status changes.
   virtual void OnIceConnectionReceivingChange(bool receiving) {}
 
   // Called when a track is added to streams.
   // TODO(zhihuang) Make this a pure virtual method when all its subclasses
   // implement it.
   virtual void OnAddTrack(
       rtc::scoped_refptr<RtpReceiverInterface> receiver,
       const std::vector<rtc::scoped_refptr<MediaStreamInterface>>& streams) {}
 
+  virtual void OnRemoveTrack(
+    rtc::scoped_refptr<RtpReceiverInterface> receiver,
+    const std::vector<rtc::scoped_refptr<MediaStreamInterface>>& streams) {}
+
  protected:
   // Dtor protected as objects shouldn't be deleted via this interface.
   ~PeerConnectionObserver() {}
 };
 
 // PeerConnectionFactoryInterface is the factory interface used for creating
 // PeerConnection, MediaStream and MediaStreamTrack objects.
 //
 // The simplest method for obtaiing one, CreatePeerConnectionFactory will
 // create the required libjingle threads, socket and network manager factory
@@ skipping 331 matching lines @@
     cricket::WebRtcVideoEncoderFactory* video_encoder_factory,
     cricket::WebRtcVideoDecoderFactory* video_decoder_factory,
     rtc::scoped_refptr<AudioMixer> audio_mixer,
     std::unique_ptr<cricket::MediaEngineInterface> media_engine,
     std::unique_ptr<CallFactoryInterface> call_factory,
     std::unique_ptr<RtcEventLogFactoryInterface> event_log_factory);
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_PEERCONNECTIONINTERFACE_H_