walk_page_dropdown_tree()

function walk_page_dropdown_tree() {
	$args = func_get_args();
	if ( empty($args[2]['walker']) ) // the user's options are the third parameter
		$walker = new Walker_PageDropdown;
	else
		$walker = $args[2]['walker'];

	return call_user_func_array(array($walker, 'walk'), $args);
}