Android: Add common function for adding/releasing native reference

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

Index: webrtc/sdk/android/api/org/webrtc/DtmfSender.java
diff --git a/webrtc/sdk/android/api/org/webrtc/DtmfSender.java b/webrtc/sdk/android/api/org/webrtc/DtmfSender.java
index 20fdd2c1ff3083ba93735a53b516e995f38375d9..d284313dcb1017f11afcbf5697bdfa3ffdd9dd76 100644
--- a/webrtc/sdk/android/api/org/webrtc/DtmfSender.java
+++ b/webrtc/sdk/android/api/org/webrtc/DtmfSender.java
@@ -71,7 +71,7 @@ public class DtmfSender {
   }
 
   public void dispose() {
-    free(nativeDtmfSender);
+    JniCommon.nativeReleaseRef(nativeDtmfSender);
   }
 
   private static native boolean nativeCanInsertDtmf(long nativeDtmfSender);
@@ -80,5 +80,4 @@ public class DtmfSender {
   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);
 };