When a track is added/removed directly to MediaStream notify observer->OnRenegotionNeeded

webrtc/pc/peerconnection.cc

Index: webrtc/pc/peerconnection.cc
diff --git a/webrtc/pc/peerconnection.cc b/webrtc/pc/peerconnection.cc
index a947c301a18461c8135106d2c85a5a8a7e582f79..17cb9fb1a34bc6a9846b23b20909da24a5182ef8 100644
--- a/webrtc/pc/peerconnection.cc
+++ b/webrtc/pc/peerconnection.cc
@@ -1555,6 +1555,7 @@ void PeerConnection::OnAudioTrackAdded(AudioTrackInterface* track,
   if (track_info) {
     new_sender->internal()->SetSsrc(track_info->ssrc);
   }
+  observer_->OnRenegotiationNeeded();
 }
 
 // TODO(deadbeef): Don't destroy RtpSenders here; they should be kept around
@@ -1572,6 +1573,7 @@ void PeerConnection::OnAudioTrackRemoved(AudioTrackInterface* track,
   }
   (*sender)->internal()->Stop();
   senders_.erase(sender);
+  observer_->OnRenegotiationNeeded();
 }
 
 void PeerConnection::OnVideoTrackAdded(VideoTrackInterface* track,
@@ -1598,6 +1600,7 @@ void PeerConnection::OnVideoTrackAdded(VideoTrackInterface* track,
   if (track_info) {
     new_sender->internal()->SetSsrc(track_info->ssrc);
   }
+  observer_->OnRenegotiationNeeded();
 }
 
 void PeerConnection::OnVideoTrackRemoved(VideoTrackInterface* track,
@@ -1613,6 +1616,7 @@ void PeerConnection::OnVideoTrackRemoved(VideoTrackInterface* track,
   }
   (*sender)->internal()->Stop();
   senders_.erase(sender);
+  observer_->OnRenegotiationNeeded();
 }
 
 void PeerConnection::PostSetSessionDescriptionFailure(