[cros] Update wallpaper when displaying Gaia frame.

chrome/browser/resources/chromeos/login/header_bar.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 Login UI header bar implementation.
  */
 
 cr.define('login', function() {
   // Network state constants.
@@ skipping 58 matching lines @@
         button.disabled = value;
       }
     },
 
     /**
      * Cancel add user button click handler.
      * @private
      */
     handleCancelAddUserClick_: function(e) {
       $('login-header-bar').signinUIActive = false;
+      $('pod-row').loadLastWallpaper();
       Oobe.showScreen({id: SCREEN_ACCOUNT_PICKER});
       Oobe.resetSigninUI(true);
     },
 
     /**
      * Guest button click handler.
      * @private
      */
     handleGuestClick_: function(e) {
       Oobe.disableSigninUI();
@@ skipping 77 matching lines @@
       $('bubble').hideForElement($('add-user-button'));
       chrome.send('loginRemoveNetworkStateObserver',
                   ['login.HeaderBar.bubbleWatchdog']);
     }
   };
 
   return {
     HeaderBar: HeaderBar
   };
 });