Android: Add common function for adding/releasing native reference

webrtc/sdk/android/src/jni/pc/mediasource_jni.cc

 /*
  *  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.
  */
 
 #include "webrtc/api/mediastreaminterface.h"
 #include "webrtc/sdk/android/src/jni/jni_helpers.h"
 
 namespace webrtc_jni {
 
-JOW(void, MediaSource_free)(JNIEnv*, jclass, jlong j_p) {
-  reinterpret_cast<rtc::RefCountInterface*>(j_p)->Release();
-}
-
 JOW(jobject, MediaSource_nativeState)(JNIEnv* jni, jclass, jlong j_p) {
   rtc::scoped_refptr<webrtc::MediaSourceInterface> p(
       reinterpret_cast<webrtc::MediaSourceInterface*>(j_p));
   return JavaEnumFromIndexAndClassName(jni, "MediaSource$State", p->state());
 }
 
 }  // namespace webrtc_jni