Android: Add common function for adding/releasing native reference

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

Index: webrtc/sdk/android/api/org/webrtc/RtpReceiver.java
diff --git a/webrtc/sdk/android/api/org/webrtc/RtpReceiver.java b/webrtc/sdk/android/api/org/webrtc/RtpReceiver.java
index d4244ed62c1dc13a259bd79b151c22d51540679f..69dfd9230f72271f3c58ac28bb14ce765dc94fb2 100644
--- a/webrtc/sdk/android/api/org/webrtc/RtpReceiver.java
+++ b/webrtc/sdk/android/api/org/webrtc/RtpReceiver.java
@@ -52,7 +52,7 @@ public class RtpReceiver {
       nativeUnsetObserver(nativeRtpReceiver, nativeObserver);
       nativeObserver = 0;
     }
-    free(nativeRtpReceiver);
+    JniCommon.nativeReleaseRef(nativeRtpReceiver);
   }
 
   public void SetObserver(Observer observer) {
@@ -74,8 +74,6 @@ public class RtpReceiver {
 
   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);