/**
  * @return html for a message to display at top of old revisions
  */
 protected function getOldRevisionHtml()
 {
     $viewSourceLink = Html::openElement('p') . Html::element('a', array('href' => '#editor/0'), $this->msg('mobile-frontend-view-source')->text()) . Html::closeElement('p');
     return $viewSourceLink . parent::getOldRevisionHtml();
 }