@Override
  public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
    return mDelegate.onFling(e1, e2, velocityX, velocityY);
  }
Wrapper for SimpleOnGestureListener as GestureDetector does not allow changing its listener.
samples/zoomable/src/main/java/com/facebook/samples/zoomable/GestureListenerWrapper.java