function validateDoubleTap() {
      if (doubleTapStartTime == null) {
        return false;
      }
      var now = getTimeStamp();
      return (hasDoubleTap() && ((now - doubleTapStartTime) <= options.doubleTapThreshold));
    }
Returns true if we could be in the process of a double tap (one tap has occurred, we are listening for double taps, and the threshold hasn't past.
@return Boolean
@inner