Instantiates the admin bar object and set it up as a global for access elsewhere.

UNHOOKING THIS FUNCTION WILL NOT PROPERLY REMOVE THE ADMIN BAR.
For that, use show_admin_bar(false) or the {@see ‘show_admin_bar’} filter.

function _wp_admin_bar_init() {
	global $wp_admin_bar;

	if ( ! is_admin_bar_showing() ) {
		return false;
	}

	/* Load the admin bar class code ready for instantiation */
	require_once ABSPATH . WPINC . '/class-wp-admin-bar.php';

	/* Instantiate the admin bar */

	/**
	 * Filters the admin bar class to instantiate.
	 *
	 * @since 3.1.0
	 *
	 * @param string $wp_admin_bar_class Admin bar class to use. Default 'WP_Admin_Bar'.
	 */
	$admin_bar_class = apply_filters( 'wp_admin_bar_class', 'WP_Admin_Bar' );
	if ( class_exists( $admin_bar_class ) ) {
		$wp_admin_bar = new $admin_bar_class;
	} else {
		return false;
	}

	$wp_admin_bar->initialize();
	$wp_admin_bar->add_menus();

	return true;
}