[cros,webui] Captive portal on login screen proper handling.

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

 // Copyright (c) 2011 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 Login UI header bar implementation.
  */
 
 cr.define('login', function() {
 
   /**
    * Creates a header bar element.
    * @constructor
    * @extends {HTMLDivElement}
    */
   var HeaderBar = cr.ui.define('div');
 
   HeaderBar.prototype = {
     __proto__: HTMLDivElement.prototype,
 
     /** @inheritDoc */
     decorate: function() {
       $('shutdown-header-bar-item').addEventListener('click',
           this.handleShutdownClick_);
       $('shutdown-button').addEventListener('click',
           this.handleShutdownClick_);
       $('add-user-button').addEventListener('click', function(e) {
-        if (window.navigator.onLine) {
-          Oobe.showSigninUI();
-        } else {
-          $('bubble').showTextForElement($('add-user-button'),
-              localStrings.getString('addUserOfflineMessage'));
-        }
+        chrome.send('loginRequestNetworkState',
+                    ['login.HeaderBar.updateState']);
       });
       $('cancel-add-user-button').addEventListener('click', function(e) {
         this.hidden = true;
         $('add-user-button').hidden = false;
         Oobe.showScreen({id: SCREEN_ACCOUNT_PICKER});
       });
     },
 
     /**
      * Shutdown button click handler.
      * @private
      */
     handleShutdownClick_: function(e) {
       chrome.send('shutdownSystem');
     }
   };
 
+  /**
+   * Network state changed callback.
+   * @param {Integer} state Current state of the network: 0 - offline;
+   * 1 - online; 2 - under the captive portal.
+   */
+  HeaderBar.updateState = function(state) {
+    var isOffline = state == 0;
+    if (!isOffline) {
+      Oobe.showSigninUI();
+    } else {
+      $('bubble').showTextForElement($('add-user-button'),
+          localStrings.getString('addUserOfflineMessage'));
+    }
+  }
+
   return {
     HeaderBar: HeaderBar
   };
 });