Adding a custom link to the WordPress Admin/Toolbar complete with icon.

wp_custom_toolbar_link.php

<?php
/*
Plugin Name: Custom Admin Bar Link
Plugin URI: http://www.creare.co.uk
Description: This simple plugin adds custom link to the Admin Bar Menu with the option of having a supporting icon.
Version: 0.1
Author: James Bavington
Author URI: https://twitter.com/jamesbavington
*/

// Check if WooCommerce is active

if ( in_array( 'woocommerce/woocommerce.php', apply_filters( 'active_plugins', get_option( 'active_plugins' ) ) ) ) {

	add_action( 'admin_bar_menu', 'custom_wp_toolbar_link', 999 );

	function custom_wp_toolbar_link( $wp_admin_bar ) {
		if( current_user_can( 'level_3' ) ){

			$args = array(
				'id' => 'woo-orders',
				'title' => '<span class="ab-icon"></span><span class="ab-label">'.__( 'Customer Orders', 'some-textdomain' ).'</span>',
				'href' => '/wp-admin/edit.php?post_type=shop_order',
				'meta' => array(
					'target' => '_self',
					'class' => 'woo-orders',
					'title' => 'View all customer orders'
				)
			);
			$wp_admin_bar->add_node($args);

		}
	}

	add_action( 'admin_enqueue_scripts', 'custom_wp_toolbar_css_admin' );
	add_action( 'wp_enqueue_scripts', 'custom_wp_toolbar_css_admin' );

	function custom_wp_toolbar_css_admin() {
		if( current_user_can( 'level_3' ) ){
		    wp_register_style( 'add_custom_wp_toolbar_css', plugin_dir_url( __FILE__ ) . 'custom-admin-link.css','','', 'screen' );
		    wp_enqueue_style( 'add_custom_wp_toolbar_css' );
		}
	}
}