Make wallpaper picker manifest and thumbnails available when offline.

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

 // Copyright (c) 2012 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.
  *
  * @constructor
  * @param {HTMLElement} dialogDom The DOM node containing the prototypical
  *     extension UI.
  */
 
 function WallpaperManager(dialogDom) {
   this.dialogDom_ = dialogDom;
+  this.storage_ = chrome.storage.local;
   this.document_ = dialogDom.ownerDocument;
   this.selectedCategory = null;
   this.butterBar_ = new ButterBar(this.dialogDom_);
   this.customWallpaperData_ = null;
   this.currentWallpaper_ = null;
   this.wallpaperRequest_ = null;
   this.fetchManifest_();
 }
 
 // Anonymous 'namespace'.
 // TODO(bshe): Get rid of anonymous namespace.
 (function() {
 
   /**
    * Base URL of the manifest file.
    */
   /** @const */ var ManifestBaseURL = 'https://commondatastorage.googleapis.' +
       'com/chromeos-wallpaper-public/manifest_';
 
   /**
    * Suffix to append to baseURL if requesting high resoultion wallpaper.
    */
   /** @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.
    * Equivilant to localStrings.getString(id).
    *
    * @param {string} id The id of the string to return.
    * @return {string} The translated string.
    */
   function str(id) {
     return loadTimeData.getString(id);
@@ skipping 59 matching lines @@
             loop.next();
           }
         });
         xhr.open('GET', url, true);
         xhr.send(null);
       } catch (e) {
         loop.failure();
       }
     };
 
-    asyncFetchManifestFromUrls(urls, fetchManifestAsync,
-                               this.onLoadManifestSuccess_.bind(this),
-                               this.onLoadManifestFailed_.bind(this));
+    if (navigator.onLine) {
+      asyncFetchManifestFromUrls(urls, fetchManifestAsync,
+                                 this.onLoadManifestSuccess_.bind(this),
+                                 this.onLoadManifestFailed_.bind(this));
+    } else {
+      // If device is offline, fetches manifest from local storage.
+      // TODO(bshe): Always loading the offline manifest first and replacing
+      // with the online one when available.
+      this.onLoadManifestFailed_();
+    }
   };
 
   /**
    * Sets manifest loaded from server. Called after manifest is successfully
    * loaded.
    * @param {object} manifest The parsed manifest file.
    */
   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'),
-                               {help_url: LEARN_MORE_URL});
-    this.initDom_();
+    var self = this;
+    this.storage_.get(AccessManifestKey, function(items) {
+      self.manifest_ = items[AccessManifestKey] ? items[AccessManifestKey] : {};
+      self.butterBar_.showError_(str('connectionFailed'),
+                                 {help_url: LEARN_MORE_URL});
+      self.initDom_();
+    });
   };
 
   /**
    * One-time initialization of various DOM nodes.
    */
   WallpaperManager.prototype.initDom_ = function() {
     i18nTemplate.process(this.document_, loadTimeData);
     this.initCategoriesList_();
     this.initThumbnailsGrid_();
 
@@ skipping 285 matching lines @@
             selectedItem = wallpaperInfo;
           }
         }
       }
       this.wallpaperGrid_.dataModel = wallpapersDataModel;
       this.wallpaperGrid_.selectedItem = selectedItem;
     }
   };
 
 })();