Fix unexpected error message when quickly select different wallpapers

chrome/browser/resources/chromeos/wallpaper_manager/js/util.js

 // Copyright (c) 2013 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.
 
 var WallpaperUtil = {};
 
 /**
  * Saves value to local storage that associates with key.
  * @param {string} key The key that associates with value.
  * @param {string} value The value to save to local storage.
@@ skipping 43 matching lines @@
   var xhr;
   if (opt_xhr)
     xhr = opt_xhr;
   else
     xhr = new XMLHttpRequest();
 
   try {
     xhr.addEventListener('loadend', function(e) {
       if (this.status == 200) {
         onSuccess(this);
+      } else if (this.status == 0) {

[flackr, 2013/09/06 15:44:00]

A status of 0 can also result from a network error it seems:
http://www.w3.org/TR/XMLHttpRequest/#the-status-attribute

I agree if the request is aborted that we shouldn't trigger an error because it
was an intentional cancellation but we should be careful not to silently fail in
other cases.

+        // The status attribute may return 0 if this request is aborted when
+        // readystate is UNSENT or OPENED. No error message should show. See
+        // http://crbug.com/242581.
+        return;
       } else {
         onFailure();
       }
     });
     xhr.open('GET', url, true);
     xhr.responseType = type;
     xhr.send(null);
   } catch (e) {
     onFailure();
   }
@@ skipping 20 matching lines @@
         chrome.wallpaperPrivate.setWallpaper(xhr.response, layout, url,
                                              onSuccess);
         self.saveWallpaperInfo(url, layout,
                                Constants.WallpaperSourceEnum.Online);
       } else {
         onFailure();
       }
     }, onFailure);
   });
 };