Fix custom wallpaper going back from wallpaper 2 to wallpaper 1

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

Index: chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.js
diff --git a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.js b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.js
index 35a0d99103cf1f581303f646577c46265264ef19..ea8e6ee8e7d51dd7a6c1874ce384fb90ef399fca 100644
--- a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.js
+++ b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.js
@@ -247,6 +247,18 @@ cr.define('wallpapers', function() {
     },
 
     /**
+     * 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() {