docs: public static int getScrollbarWidth() {
  
          if (m_scrollbarWidth == -1) {
              Element div = DOM.createDiv();
              div.setAttribute("style", "width:100px; height:100px; overflow: scroll; position:absolute; top:-9999px;");
              RootPanel.getBodyElement().appendChild(div);
              m_scrollbarWidth = div.getOffsetWidth() - div.getClientWidth();
              div.removeFromParent();
          }
          return m_scrollbarWidth;
      }