Source

File: wp-includes/class-wp-admin-bar.php

public function initialize() {
		$this->user = new stdClass;

		if ( is_user_logged_in() ) {
			/* Populate settings we need for the menu based on the current user. */
			$this->user->blogs = get_blogs_of_user( get_current_user_id() );
			if ( is_multisite() ) {
				$this->user->active_blog    = get_active_blog_for_user( get_current_user_id() );
				$this->user->domain         = empty( $this->user->active_blog ) ? user_admin_url() : trailingslashit( get_home_url( $this->user->active_blog->blog_id ) );
				$this->user->account_domain = $this->user->domain;
			} else {
				$this->user->active_blog    = $this->user->blogs[ get_current_blog_id() ];
				$this->user->domain         = trailingslashit( home_url() );
				$this->user->account_domain = $this->user->domain;
			}
		}

		add_action( 'wp_head', 'wp_admin_bar_header' );

		add_action( 'admin_head', 'wp_admin_bar_header' );

		if ( current_theme_supports( 'admin-bar' ) ) {
			/**
			 * To remove the default padding styles from WordPress for the Toolbar, use the following code:
			 * add_theme_support( 'admin-bar', array( 'callback' => '__return_false' ) );
			 */
			$admin_bar_args  = get_theme_support( 'admin-bar' );
			$header_callback = $admin_bar_args[0]['callback'];
		}

		if ( empty( $header_callback ) ) {
			$header_callback = '_admin_bar_bump_cb';
		}

		add_action( 'wp_head', $header_callback );

		wp_enqueue_script( 'admin-bar' );
		wp_enqueue_style( 'admin-bar' );

		/**
		 * Fires after WP_Admin_Bar is initialized.
		 *
		 * @since 3.1.0
		 */
		do_action( 'admin_bar_init' );
	}