Fix custom wallpaper going back from wallpaper 2 to wallpaper 1

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 752 matching lines @@
                 var wallpaperInfo = {
                   baseURL: fileName,
                   layout: layout,
                   source: wallpapers.WallpaperSourceEnum.Custom,
                   availableOffline: true
                 };
                 self.currentWallpaper_ = fileName;
                 var items = {};
                 items[self.currentWallpaper_] = layout;
                 self.storage_.set(items, function() {});
-                self.wallpaperGrid_.dataModel.splice(0, 0, wallpaperInfo);
+                self.wallpaperGrid_.insertElement(0, wallpaperInfo);
                 self.wallpaperGrid_.selectedItem = wallpaperInfo;
                 self.wallpaperGrid_.activeItem = wallpaperInfo;
               };
 
               fileWriter.onerror = errorHandler;
 
               var blob = new Blob([new Int8Array(thumbnail)],
                                   {'type' : 'image\/jpeg'});
               fileWriter.write(blob);
             }, errorHandler);
@@ skipping 233 matching lines @@
           }
         }
       }
       this.wallpaperGrid_.dataModel = wallpapersDataModel;
       this.wallpaperGrid_.selectedItem = selectedItem;
       this.wallpaperGrid_.activeItem = selectedItem;
     }
   };
 
 })();