Android: Add common function for adding/releasing native reference

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

 /*
  *  Copyright 2017 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 53 matching lines @@
   /**
    * @return The current value of the between-tone gap in ms. This value will be the value last set
    *         via the insertDtmf() method, or the default value of 50 ms if insertDtmf() was never
    *         called.
    */
   public int interToneGap() {
     return nativeInterToneGap(nativeDtmfSender);
   }
 
   public void dispose() {
-    free(nativeDtmfSender);
+    JniCommon.nativeReleaseRef(nativeDtmfSender);
   }
 
   private static native boolean nativeCanInsertDtmf(long nativeDtmfSender);
   private static native boolean nativeInsertDtmf(
       long nativeDtmfSender, String tones, int duration, int interToneGap);
   private static native String nativeTones(long nativeDtmfSender);
   private static native int nativeDuration(long nativeDtmfSender);
   private static native int nativeInterToneGap(long nativeDtmfSender);
-  private static native void free(long nativeDtmfSender);
 };