Add PeerConnectionObserver#onRemoveTrack to android sdk

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

 /*
  *  Copyright 2013 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 34 matching lines @@
   public State state() {
     return nativeState(nativeTrack);
   }
 
   public void dispose() {
     free(nativeTrack);
   }
 
   private static native String nativeId(long nativeTrack);
 
-  private static native String nativeKind(long nativeTrack);
+  static native String nativeKind(long nativeTrack);
 
   private static native boolean nativeEnabled(long nativeTrack);
 
   private static native boolean nativeSetEnabled(long nativeTrack, boolean enabled);
 
   private static native State nativeState(long nativeTrack);
 
   private static native void free(long nativeTrack);
 }