google search in menu bar

add_filter('wp_nav_menu_items','add_search_box', 10, 2);
function add_search_box($items, $args) {
    if($args->theme_location == 'header-menu') {
        ob_start();
        display_search_box(DISPLAY_RESULTS_AS_POP_UP);
        $searchform = ob_get_contents();
        ob_end_clean();

        return $items .= '<li id="searchform-item">' . $searchform . '</li>';
    }
    return $items;
}