Fix custom wallpaper going back from wallpaper 2 to wallpaper 1

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.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.
 
 cr.define('wallpapers', function() {
   /** @const */ var ArrayDataModel = cr.ui.ArrayDataModel;
   /** @const */ var Grid = cr.ui.Grid;
   /** @const */ var GridItem = cr.ui.GridItem;
   /** @const */ var GridSelectionController = cr.ui.GridSelectionController;
   /** @const */ var ListSingleSelectionModel = cr.ui.ListSingleSelectionModel;
@@ skipping 229 matching lines @@
     },
     set selectedItem(selectedItem) {
       var index = this.dataModel.indexOf(selectedItem);
       this.inProgramSelection_ = true;
       this.selectionModel.leadIndex = index;
       this.selectionModel.selectedIndex = index;
       this.inProgramSelection_ = false;
     },
 
     /**
+     * The previous selected item.
+     * @type {!Object} Wallpaper information in the data model.
+     */
+    previousSelectedItem_: undefined,
+    get previousSelectedItem() {
+      return this.previousSelectedItem_;
+    },
+    set previousSelectedItem(selectedItem) {
+      this.previousSelectedItem_ = selectedItem;
+    },
+
+    /**
      * Forces re-display, size re-calculation and focuses grid.
      */
     updateAndFocus: function() {
       // Recalculate the measured item size.
       this.measured_ = null;
       this.columns = 0;
       this.redraw();
       this.focus();
     },
 
@@ skipping 27 matching lines @@
       // to make sure checkmark shows correctly.
       this.updateActiveThumb_();
     }
   };
 
   return {
     WallpaperSourceEnum: WallpaperSourceEnum,
     WallpaperThumbnailsGrid: WallpaperThumbnailsGrid
   };
 });