[cros,login] Prevent WebUI race, when network drop-down is hided.

chrome/browser/resources/chromeos/login/network_dropdown.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 Network drop-down implementation.
  */
 
 cr.define('cr.ui', function() {
   /**
@@ skipping 336 matching lines @@
         }
       }
     }
   };
 
   /**
    * Updates networks list with the new data.
    * @param {!Object} data Networks list.
    */
   DropDown.updateNetworks = function(data) {
-    var elementId = DropDown.activeElementId_;
-    $(elementId).setItems(data);
+    if (DropDown.activeElementId_)
+      $(DropDown.activeElementId_).setItems(data);
   };
 
   /**
    * Updates network title, which is shown by the drop-down.
    * @param {string} title Title to be displayed.
    * @param {!Object} icon Icon to be displayed.
    */
   DropDown.updateNetworkTitle = function(title, icon) {
-    var elementId = DropDown.activeElementId_;
-    $(elementId).setTitle(title, icon);
+    if (DropDown.activeElementId_)
+      $(DropDown.activeElementId_).setTitle(title, icon);
   };
 
   /**
    * Activates or deactivates network drop-down. Only one network drop-down
    * can be active at the same time. So activating new drop-down deactivates
    * the previous one. Deactivating not active drop-down does nothing.
    * @param {string} element_id Id of the element which is network drop-down.
    * @param {boolean} isActive Is drop-down active?
    * @param {boolean} isOobe Is dropdown placed on an OOBE screen.
    */
   DropDown.setActive = function(elementId, isActive, isOobe) {
     if (isActive) {
-      DropDown.activeElementId_ = elementId;
       $(elementId).isShown = false;
-      chrome.send('networkDropdownShow', [elementId, isOobe]);
+      if (DropDown.activeElementId_ != elementId) {
+        DropDown.activeElementId_ = elementId;
+        chrome.send('networkDropdownShow', [elementId, isOobe]);
+      }
     } else {
       if (DropDown.activeElementId_ == elementId) {
         DropDown.activeElementId_ = '';
         chrome.send('networkDropdownHide', []);
       }
     }
   };
 
   /**
    * Refreshes network drop-down. Should be called on language change.
    */
   DropDown.refresh = function() {
     chrome.send('networkDropdownRefresh', []);
   };
 
   return {
     DropDown: DropDown
   };
 });