WordPress at a glance
function is not described

wp_admin_bar_search_menu() WP 3.3.0

Add search form.

No Hooks.

Return

Nothing (null).

Usage

wp_admin_bar_search_menu( $wp_admin_bar );
$wp_admin_bar(WP_Admin_Bar) (required)

Code of wp admin bar search menu: wp-includes/admin-bar.php VER 5.0.3

<?php
function wp_admin_bar_search_menu( $wp_admin_bar ) {
	if ( is_admin() )
		return;

	$form  = '<form action="' . esc_url( home_url( '/' ) ) . '" method="get" id="adminbarsearch">';
	$form .= '<input class="adminbar-input" name="s" id="adminbar-search" type="text" value="" maxlength="150" />';
	$form .= '<label for="adminbar-search" class="screen-reader-text">' . __( 'Search' ) . '</label>';
	$form .= '<input type="submit" class="adminbar-button" value="' . __('Search') . '"/>';
	$form .= '</form>';

	$wp_admin_bar->add_menu( array(
		'parent' => 'top-secondary',
		'id'     => 'search',
		'title'  => $form,
		'meta'   => array(
			'class'    => 'admin-bar-search',
			'tabindex' => -1,
		)
	) );
}