code: public void addClearListButton(ClickHandler clickHandler) {
  
          m_clearButton = new CmsPushButton();
          m_clearButton.setText(Messages.get().key(Messages.GUI_CLIPBOARD_CLEAR_LIST_0));
          m_clearButton.setTitle(Messages.get().key(Messages.GUI_CLIPBOARD_CLEAR_LIST_0));
          m_clearButton.addClickHandler(clickHandler);
          m_clearButton.addStyleName(I_CmsSitemapLayoutBundle.INSTANCE.clipboardCss().listClearButton());
          m_panel.add(m_clearButton);
      }
docs: Adds a clear list button to the tab.<p>
  
  @param clickHandler the button click handler