Make wallpaper picker manifest and thumbnails available when offline.

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

Index: chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
diff --git a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
index d91616bf96075d7a458a40ccde14853adcb5381b..161590c710dfb3e069f8197ee15c0b4fbf4710bf 100644
--- a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
+++ b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
@@ -15,6 +15,7 @@
 
 function WallpaperManager(dialogDom) {
   this.dialogDom_ = dialogDom;
+  this.storage_ = chrome.storage.local;
   this.document_ = dialogDom.ownerDocument;
   this.selectedCategory = null;
   this.butterBar_ = new ButterBar(this.dialogDom_);
@@ -40,6 +41,11 @@ function WallpaperManager(dialogDom) {
   /** @const */ var HighResolutionSuffix = '_high_resolution.jpg';
 
   /**
+   * Key to access wallpaper manifest in chrome.local.storage.
+   */
+  /** @const */ var AccessManifestKey = 'wallpaper-picker-manifest-key';
+
+  /**
    * Returns a translated string.
    *
    * Wrapper function to make dealing with translated strings more concise.
@@ -131,17 +137,21 @@ function WallpaperManager(dialogDom) {
    */
   WallpaperManager.prototype.onLoadManifestSuccess_ = function(manifest) {
     this.manifest_ = manifest;
+    var items = {};
+    items[AccessManifestKey] = manifest;
+    this.storage_.set(items, function() {});
     this.initDom_();
   };
 
-  // Sets manifest to an empty object and shows connection error. Called after
-  // manifest failed to load.
+  // Sets manifest to previously saved object if any and shows connection error.
+  // Called after manifest failed to load.
   WallpaperManager.prototype.onLoadManifestFailed_ = function() {
-    // TODO(bshe): Fall back to saved manifest if there is a problem fetching
-    // manifest from server.
-    this.manifest_ = {};
-    this.butterBar_.showError_(str('connectionFailed'));
-    this.initDom_();
+    var self = this;
+    this.storage_.get(AccessManifestKey, function(items) {
+      self.manifest_ = items[AccessManifestKey] ? items[AccessManifestKey] : {};
+      self.butterBar_.showError_(str('connectionFailed'));
+      self.initDom_();
+    });
   };
 
   /**