WordPress at a glance
function is not described

wp_admin_bar_sidebar_toggle() WP 3.8.0

Add the sidebar toggle button.

No Hooks.

Return

Nothing (null).

Usage

wp_admin_bar_sidebar_toggle( $wp_admin_bar );
$wp_admin_bar(WP_Admin_Bar) (required)

Code of wp admin bar sidebar toggle: wp-includes/admin-bar.php VER 5.1.1

<?php
function wp_admin_bar_sidebar_toggle( $wp_admin_bar ) {
	if ( is_admin() ) {
		$wp_admin_bar->add_menu(
			array(
				'id'    => 'menu-toggle',
				'title' => '<span class="ab-icon"></span><span class="screen-reader-text">' . __( 'Menu' ) . '</span>',
				'href'  => '#',
			)
		);
	}
}