Add an option to set the default value to the current date.
Overrides ArgumentPluginBase::defaultArgumentForm
public function defaultArgumentForm(&$form, &$form_state) {
parent::defaultArgumentForm($form, $form_state);
$form['default_argument_type']['#options'] += array(
'date' => t('Current date'),
);
$form['default_argument_type']['#options'] += array(
'node_created' => t("Current node's creation time"),
);
$form['default_argument_type']['#options'] += array(
'node_changed' => t("Current node's update time"),
);
}