Add onRemoveTrack for Android.

AUTHORS

@@ -53,6 +53,7 @@ James H. Brown <jbrown@burgoyne.com>
 Jan Grulich <grulja@gmail.com>
 Jan Kalab <pitlicek@gmail.com>
 Jens Nielsen <jens.nielsen@berotec.se>
+Jesús Leganés-Combarro <piranna@gmail.com>
 Jiawei Ou <jiawei.ou@gmail.com>
 Jie Mao <maojie0924@gmail.com>
 Jiwon Kim <jwkim0000@gmail.com>

examples/androidapp/src/org/appspot/apprtc/PeerConnectionClient.java

@@ -1316,6 +1316,9 @@ public void onRenegotiationNeeded() {
 
     @Override
     public void onAddTrack(final RtpReceiver receiver, final MediaStream[] mediaStreams) {}
+
+    @Override
+    public void onRemoveTrack(final RtpReceiver receiver) {}
   }
 
   // Implementation detail: handle offer creation/signaling and answer setting,

sdk/android/api/org/webrtc/PeerConnection.java

@@ -141,7 +141,14 @@ default void onSelectedCandidatePairChanged(CandidatePairChangeEvent event) {}
      * Triggered when a new track is signaled by the remote peer, as a result of
      * setRemoteDescription.
      */
-    @CalledByNative("Observer") void onAddTrack(RtpReceiver receiver, MediaStream[] mediaStreams);
+    @CalledByNative("Observer")
+    default void onAddTrack(RtpReceiver receiver, MediaStream[] mediaStreams){};
+
+    /**
+     * Triggered when a previously added remote track is removed by the remote
+     * peer, as a result of setRemoteDescription.
+     */
+    @CalledByNative("Observer") default void onRemoveTrack(RtpReceiver receiver){};
 
     /**
      * Triggered when the signaling from SetRemoteDescription indicates that a transceiver

sdk/android/src/jni/pc/peer_connection.cc

@@ -410,6 +410,16 @@ void PeerConnectionObserverJni::OnAddTrack(
                            NativeToJavaMediaStreamArray(env, streams));
 }
 
+void PeerConnectionObserverJni::OnRemoveTrack(
+    rtc::scoped_refptr<RtpReceiverInterface> receiver) {
+  JNIEnv* env = AttachCurrentThreadIfNeeded();
+  ScopedJavaLocalRef<jobject> j_rtp_receiver =
+      NativeToJavaRtpReceiver(env, receiver);
+  rtp_receivers_.emplace_back(env, j_rtp_receiver);
+
+  Java_Observer_onRemoveTrack(env, j_observer_global_, j_rtp_receiver);
+}
+
 void PeerConnectionObserverJni::OnTrack(
     rtc::scoped_refptr<RtpTransceiverInterface> transceiver) {
   JNIEnv* env = AttachCurrentThreadIfNeeded();

sdk/android/src/jni/pc/peer_connection.h

@@ -72,6 +72,8 @@ class PeerConnectionObserverJni : public PeerConnectionObserver {
                       streams) override;
   void OnTrack(
       rtc::scoped_refptr<RtpTransceiverInterface> transceiver) override;
+  void OnRemoveTrack(
+      rtc::scoped_refptr<RtpReceiverInterface> receiver) override;
 
  private:
   typedef std::map<MediaStreamInterface*, JavaMediaStream>