Improve accessible markup of OOBE network drop-down.

chrome/browser/resources/chromeos/login/network_dropdown.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview Network drop-down implementation.
  */
 
 cr.define('cr.ui', function() {
   /**
@@ skipping 75 matching lines @@
   DropDown.KEYCODE_TAB = 9;
   DropDown.KEYCODE_UP = 38;
 
   DropDown.prototype = {
     __proto__: HTMLDivElement.prototype,
 
     /** @override */
     decorate: function() {
       this.appendChild(this.createOverlay_());
       this.appendChild(this.title_ = this.createTitle_());
-      this.appendChild(new DropDownContainer());
+      var container = new DropDownContainer();
+      container.id = this.id + '-dropdown-container';
+      this.appendChild(container);
 
       this.addEventListener('keydown', this.keyDownHandler_);
 
       this.title_.id = this.id + '-dropdown';
       this.title_.setAttribute('role', 'button');
       this.title_.setAttribute('aria-haspopup', 'true');
+      this.title_.setAttribute('aria-owns', container.id);
     },
 
     /**
      * Returns true if dropdown menu is shown.
      * @type {bool} Whether menu element is shown.
      */
     get isShown() {
       return !this.container.hidden;
     },
 
     /**
      * Sets dropdown menu visibility.
      * @param {bool} show New visibility state for dropdown menu.
      */
     set isShown(show) {
       this.firstElementChild.hidden = !show;
       this.container.hidden = !show;
       if (show) {
         this.container.selectItem(this.container.firstItem, false);
-        this.title_.setAttribute('aria-pressed', 'true');
       } else {
-        this.title_.setAttribute('aria-pressed', 'false');
         this.title_.removeAttribute('aria-activedescendant');
       }
     },
 
     /**
      * Returns title button.
      */
     get titleButton() {
       return this.children[1];
     },
@@ skipping 276 matching lines @@
    * Refreshes network drop-down. Should be called on language change.
    */
   DropDown.refresh = function() {
     chrome.send('networkDropdownRefresh');
   };
 
   return {
     DropDown: DropDown
   };
 });