Convert wallpaper picker to v2 app

chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_images_grid.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.
 
 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 14 matching lines @@
     return el;
   }
 
   WallpaperThumbnailsGridItem.prototype = {
     __proto__: GridItem.prototype,
 
     /** @inheritDoc */
     decorate: function() {
       GridItem.prototype.decorate.call(this);
       var imageEl = cr.doc.createElement('img');
-      // Thumbnail
-      imageEl.src = this.dataItem.baseURL + ThumbnailSuffix;
-      // Remove any garbage added by GridItem and ListItem decorators.
-      this.textContent = '';
-      this.appendChild(imageEl);
+      var xhr = new XMLHttpRequest();
+      xhr.open('GET', this.dataItem.baseURL + ThumbnailSuffix, true);

[Mihai Parparita -not on Chrome, 2012/10/12 00:48:47]

What is the base URL in this case? We generally are OK with loading of local
images (they don't have issues when offline).

[bshe, 2012/10/12 16:28:30]

The base URL is a online url.
https://storage.googleapis.com/chromeos-wallpaper-public/timestamp-file-name.png

We want to push new wallpapers to users as soon as possible. If we include them
as local iamges, users will have to wait for chrome update to get the new
wallpapers.

On 2012/10/12 00:48:47, Mihai Parparita wrote:

+      xhr.responseType = 'blob';
+      xhr.send(null);
+      var self = this;
+      xhr.addEventListener('load', function(e) {
+        if (xhr.status === 200) {
+          self.textContent = '';
+          imageEl.src = window.URL.createObjectURL(xhr.response);

[Mihai Parparita -not on Chrome, 2012/10/12 00:48:47]

This will leak the URL, you'll need to call revokeObjectURL once the window is
closing.

[bshe, 2012/10/12 16:28:30]

I saw examples of revoke object after load. After test on my desktop, it seems
work fine. We just need to display the thumbnail and wont do any manipulation on
the URL object after load. So it is probably fine to just revoke them after
load?

On 2012/10/12 00:48:47, Mihai Parparita wrote:

+          self.appendChild(imageEl);
+        }
+        //TODO(bshe): Add error handleing.
+      });
     },
   };
 
   /**
    * Creates a selection controller that wraps selection on grid ends
    * and translates Enter presses into 'activate' events.
    * @param {cr.ui.ListSelectionModel} selectionModel The selection model to
    *     interact with.
    * @param {cr.ui.Grid} grid The grid to interact with.
    * @constructor
@@ skipping 98 matching lines @@
       this.columns = 0;
       this.redraw();
       this.focus();
     }
   };
 
   return {
     WallpaperThumbnailsGrid: WallpaperThumbnailsGrid
   };
 });