Enable user change background image in settings page in Aura build.

chrome/browser/resources/options2/options.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.
 
 var AddLanguageOverlay = options.AddLanguageOverlay;
 var AlertOverlay = options.AlertOverlay;
 var AutofillEditAddressOverlay = options.AutofillEditAddressOverlay;
 var AutofillEditCreditCardOverlay = options.AutofillEditCreditCardOverlay;
 var AutofillOptions = options.AutofillOptions;
 var BrowserOptions = options.BrowserOptions;
@@ skipping 103 matching lines @@
   OptionsPage.registerOverlay(SearchEngineManager.getInstance(),
                               BrowserOptions.getInstance(),
                               [$('manage-default-search-engines')]);
   OptionsPage.registerOverlay(SessionRestoreOverlay.getInstance(),
                               BrowserOptions.getInstance());
   OptionsPage.registerOverlay(StartupOverlay.getInstance(),
                               BrowserOptions.getInstance());
   OptionsPage.registerOverlay(SyncSetupOverlay.getInstance(),
                               BrowserOptions.getInstance());
   if (cr.isChromeOS) {
+    OptionsPage.registerOverlay(SetWallpaperOptions.getInstance(),
+                                BrowserOptions.getInstance(),
+                                [$('set-wallpaper')]);

[flackr, 2012/03/05 16:16:03]

This also concerns me, I'm pretty sure that options will be broken on ChromeOS
non-aura (chromeos_gtk=1) and this won't be registered if we support an aura
non-chromeos build.

[bshe, 2012/03/06 01:33:27]

Done
check the existence of SetWallpaperOptions here to be safer.

     OptionsPage.registerOverlay(AccountsOptions.getInstance(),
                                 BrowserOptions.getInstance(),
                                 [$('manage-accounts-button')]);
     OptionsPage.registerOverlay(BluetoothOptions.getInstance(),
                                 BrowserOptions.getInstance(),
                                 [$('bluetooth-add-device')]);
     OptionsPage.registerOverlay(BluetoothPairing.getInstance(),
                                 BrowserOptions.getInstance());
     OptionsPage.registerOverlay(ChangePictureOptions.getInstance(),
                                 BrowserOptions.getInstance(),
@@ skipping 98 matching lines @@
   options.OptionsPage.willClose();
 };
 
 /**
  * Listener for the |popstate| event.
  * @param {Event} e The |popstate| event.
  */
 window.onpopstate = function(e) {
   options.OptionsPage.setState(e.state);
 };