code: public TouchActions scroll(WebElement onElement, int xOffset, int yOffset) {
      if (touchScreen != null) {
        action.addAction(new ScrollAction(touchScreen, (Locatable) onElement, xOffset, yOffset));
      }
      return this;
    }
docs: Creates a scroll gesture that starts on a particular screen location.
  
  @param onElement the {@link WebElement} where the scroll starts.
  @param xOffset   The x offset to scroll
  @param yOffset   The y offset to scroll
  @return self