code: private void setScrollingSelector(int availableHeight) {
  
          CmsScrollPanel panel = GWT.create(CmsScrollPanel.class);
          panel.getElement().getStyle().setHeight(availableHeight, Unit.PX);
          panel.setWidget(m_selector);
          m_popup.setWidget(panel);
      }
docs: Adds a scroll panel to the selector popup.<p>
  
  @param availableHeight the available popup height