Fix the issue that wallpaper changes twice when both "onChanged" and "onAlarm" are fired.

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.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.
 
 /**
  * WallpaperManager constructor.
  *
  * WallpaperManager objects encapsulate the functionality of the wallpaper
  * manager extension.
  *
@@ skipping 578 matching lines @@
                 });
             WallpaperUtil.saveWallpaperInfo(wallpaperURL, selectedItem.layout,
                                             selectedItem.source);
             self.wallpaperRequest_ = null;
           };
           var onFailure = function() {
             self.progressManager_.hideProgressBar(selectedGridItem);
             self.showError_(str('downloadFailed'));
             self.wallpaperRequest_ = null;
           };
-          WallpaperUtil.fetchURL(wallpaperURL, 'arraybuffer', onSuccess,
-                                 onFailure, self.wallpaperRequest_);
+          WallpaperUtil.fetchURL(wallpaperURL, 'arraybuffer',
+                                 onSuccess, onFailure, function() {},
+                                 self.wallpaperRequest_);
         });
         break;
       default:
         console.error('Unsupported wallpaper source.');
     }
   };
 
   /*
    * Removes the oldest custom wallpaper. If the oldest one is set as current
    * wallpaper, removes the second oldest one to free some space. This should
@@ skipping 480 matching lines @@
       }
       this.wallpaperGrid_.dataModel = wallpapersDataModel;
       if (selectedItem) {
         this.wallpaperGrid_.selectedItem = selectedItem;
         this.wallpaperGrid_.activeItem = selectedItem;
       }
     }
   };
 
 })();