Disable wallpaper button in Guest mode settings

chrome/browser/resources/options/browser_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.
 
 cr.exportPath('options');
 
 /**
  * @typedef {{actionLinkText: (string|undefined),
  *            hasError: (boolean|undefined),
  *            hasUnrecoverableError: (boolean|undefined),
@@ skipping 1490 matching lines @@
       if (picture) {
         picture.src = 'chrome://userimage/' + this.username_ + '?id=' +
             Date.now();
       }
     },
 
     /**
      * @param {boolean} managed
      */
     setWallpaperManaged_: function(managed) {
-      var button = $('set-wallpaper');
-      button.disabled = !!managed;
+      if (managed)
+        $('set-wallpaper').disabled = true;
+      else
+        this.enableElementIfPossible_($('set-wallpaper'));
 
       // Create a synthetic pref change event decorated as
       // CoreOptionsHandler::CreateValueForPref() does.
       var event = new Event('wallpaper');
-      if (managed)
-        event.value = { controlledBy: 'policy' };
-      else
-        event.value = {};
+      event.value = managed ? { controlledBy: 'policy' } : {};
       $('wallpaper-indicator').handlePrefChange(event);
     },
 
     /**
      * Handle the 'add device' button click.
      * @private
      */
     handleAddBluetoothDevice_: function() {
       chrome.send('findBluetoothDevices');
       PageManager.showPageByName('bluetooth', false);
@@ skipping 430 matching lines @@
       $('set-time').hidden = !canSetTime;
     },
 
     /**
      * Handle the 'set date and time' button click.
      * @private
      */
     handleSetTime_: function() {
       chrome.send('showSetTime');
     },
+
+    /**
+     * Enables the given element if possible; on Chrome OS, it won't enable
+     * an element that must stay disabled for the session type.
+     * @param {!Element} element Element to enable.
+     */
+    enableElementIfPossible_: function(element) {
+      if (cr.isChromeOS)
+        UIAccountTweaks.enableElementIfPossible(element);
+      else
+        element.disabled = false;
+    },
   };
 
   //Forward public APIs to private implementations.
   cr.makePublic(BrowserOptions, [
     'addBluetoothDevice',
     'deleteCurrentProfile',
     'enableCertificateButton',
     'enableDisplayButton',
     'enableFactoryResetSection',
     'getCurrentProfile',
@@ skipping 85 matching lines @@
       }
       button.textContent = loadTimeData.getString(strId);
     };
   }
 
   // Export
   return {
     BrowserOptions: BrowserOptions
   };
 });