public static function preRenderDropbutton($element) {
$element = parent::preRenderDropbutton($element);
// Attach #ajax events if title is a render array.
foreach ($element['#links'] as &$link) {
if (isset($link['title']['#ajax'])) {
$link['title'] = RenderElement::preRenderAjaxForm($link['title']);
}
}
return $element;
}