Android: Add common function for adding/releasing native reference

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

 /*
  *  Copyright 2015 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 String id() {
     return nativeId(nativeRtpReceiver);
   }
 
   public void dispose() {
     cachedTrack.dispose();
     if (nativeObserver != 0) {
       nativeUnsetObserver(nativeRtpReceiver, nativeObserver);
       nativeObserver = 0;
     }
-    free(nativeRtpReceiver);
+    JniCommon.nativeReleaseRef(nativeRtpReceiver);
   }
 
   public void SetObserver(Observer observer) {
     // Unset the existing one before setting a new one.
     if (nativeObserver != 0) {
       nativeUnsetObserver(nativeRtpReceiver, nativeObserver);
     }
     nativeObserver = nativeSetObserver(nativeRtpReceiver, observer);
   }
 
   // This should increment the reference count of the track.
   // Will be released in dispose().
   private static native long nativeGetTrack(long nativeRtpReceiver);
 
   private static native boolean nativeSetParameters(
       long nativeRtpReceiver, RtpParameters parameters);
 
   private static native RtpParameters nativeGetParameters(long nativeRtpReceiver);
 
   private static native String nativeId(long nativeRtpReceiver);
 
-  private static native void free(long nativeRtpReceiver);
-
   private static native long nativeSetObserver(long nativeRtpReceiver, Observer observer);
 
   private static native long nativeUnsetObserver(long nativeRtpReceiver, long nativeObserver);
 };