Android: Add common function for adding/releasing native reference

webrtc/sdk/android/src/java/org/webrtc/WrappedNativeI420Buffer.java

Index: webrtc/sdk/android/src/java/org/webrtc/WrappedNativeI420Buffer.java
diff --git a/webrtc/sdk/android/src/java/org/webrtc/WrappedNativeI420Buffer.java b/webrtc/sdk/android/src/java/org/webrtc/WrappedNativeI420Buffer.java
index 8a3186934d73b35644e549bc140ec36fe3e015e3..85d02e679237d43311fd5c7690c0eaa959105458 100644
--- a/webrtc/sdk/android/src/java/org/webrtc/WrappedNativeI420Buffer.java
+++ b/webrtc/sdk/android/src/java/org/webrtc/WrappedNativeI420Buffer.java
@@ -89,12 +89,12 @@ class WrappedNativeI420Buffer implements VideoFrame.I420Buffer {
 
   @Override
   public void retain() {
-    nativeAddRef(nativeBuffer);
+    JniCommon.nativeAddRef(nativeBuffer);
   }
 
   @Override
   public void release() {
-    nativeRelease(nativeBuffer);
+    JniCommon.nativeReleaseRef(nativeBuffer);
   }
 
   @Override
@@ -103,7 +103,4 @@ class WrappedNativeI420Buffer implements VideoFrame.I420Buffer {
     return VideoFrame.cropAndScaleI420(
         this, cropX, cropY, cropWidth, cropHeight, scaleWidth, scaleHeight);
   }
-
-  private static native long nativeAddRef(long nativeBuffer);
-  private static native long nativeRelease(long nativeBuffer);
 }