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

chrome/browser/resources/chromeos/wallpaper_manager/js/event_page.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 WALLPAPER_PICKER_WIDTH = 574;
 var WALLPAPER_PICKER_HEIGHT = 420;
 
 var wallpaperPickerWindow;
 
 var surpriseWallpaper = null;
@@ skipping 285 matching lines @@
             WallpaperUtil.setOnlineWallpaper(newValue.url, newValue.layout,
               function() {}, function() {});
           } else if (newValue.source == Constants.WallpaperSourceEnum.Custom) {
             WallpaperUtil.setCustomWallpaperFromSyncFS(newValue.url,
                                                        newValue.layout);
           } else if (newValue.source == Constants.WallpaperSourceEnum.Default) {
             chrome.wallpaperPrivate.resetWallpaper();
           }
           WallpaperUtil.saveToStorage(Constants.AccessLocalWallpaperInfoKey,
                                       newValue, false);
+          WallpaperUtil.saveToStorage(
+            Constants.AccessLastSurpriseWallpaperChangedDate,
+            dateString, true);

[bshe, 2015/02/27 19:31:19]

dateString seems undefined?

         }
       });
     }
   });
 });
 
 chrome.alarms.onAlarm.addListener(function() {
   SurpriseWallpaper.getInstance().next();
 });