Android: Add common function for adding/releasing native reference

webrtc/sdk/android/src/java/org/webrtc/JniCommon.java

Index: webrtc/sdk/android/src/java/org/webrtc/JniCommon.java
diff --git a/webrtc/sdk/android/src/java/org/webrtc/JniCommon.java b/webrtc/sdk/android/src/java/org/webrtc/JniCommon.java
new file mode 100644
index 0000000000000000000000000000000000000000..cc80becef3b97cbf7c1564c6360a92ae378aa6fe
--- /dev/null
+++ b/webrtc/sdk/android/src/java/org/webrtc/JniCommon.java
@@ -0,0 +1,18 @@
+/*
+ *  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.
+ */
+
+package org.webrtc;
+
+/** Class with static JNI helper functions that are used in many places. */
+class JniCommon {
+  /** Functions to increment/decrement an rtc::RefCountInterface pointer. */
+  static native void nativeAddRef(long nativeRefCountedPointer);
+  static native void nativeReleaseRef(long nativeRefCountedPointer);
+}