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 1474 matching lines @@
       if (picture) {
         picture.src = 'chrome://userimage/' + this.username_ + '?id=' +
             Date.now();
       }
     },
 
     /**
      * @param {boolean} managed
      */
     setWallpaperManaged_: function(managed) {
-      var button = $('set-wallpaper');
-      button.disabled = !!managed;
+      this.setElementEnabled_($('set-wallpaper'), !managed);
 
       // 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 = {};
       $('wallpaper-indicator').handlePrefChange(event);
     },
@@ skipping 425 matching lines @@
       $('set-time').hidden = !canSetTime;
     },
 
     /**
      * Handle the 'set date and time' button click.
      * @private
      */
     handleSetTime_: function() {
       chrome.send('showSetTime');
     },
+
+    /**
+     * Enables or disables the given element. On Chrome OS, this uses
+     * UIAccountTweaks so we don't enable an element that must stay disabled.
+     * @param {!Element} element Element to enable or disable.
+     * @param {boolean} enabled Whether to enable or disable the element.
+     */
+    setElementEnabled_: function(element, enabled) {
+      if (!cr.isChromeOS || !enabled)

[stevenjb, 2014/09/25 15:45:33]

Putting !cr.isChromeOS in a method called simply 'setElementEnabled_' is pretty
confusing. I'm not familiar enough with UIAccountTweaks to suggest the best
thing to do here is, but unless we use this same pattern elsewhere I might
suggest leaving the logic in setWallpaperManaged_. 
I would also suggest inverting this conditional.

[michaelpg, 2014/09/29 18:50:56]

We really should use this every time we enable/disable an element on Chrome OS
in case that element has a guest-visibility or public-account-visibility
attribute. So I think we should move to using this function in more places, to
prevent more bugs like this from arising.

Some elements, e.g. in plugins.html, have a *-visibility attribute but are not
Chrome OS-only. So I could rename this function, and then wherever we want to
disable an element we would say:

if (cr.isChromeOS)
  this.setElementEnabledIfAllowed(element, false);
else
  element.disabled = true;

+        element.disabled = !enabled;
+      else
+        UIAccountTweaks.enableElementIfPossible(element);
+    },
   };
 
   //Forward public APIs to private implementations.
   cr.makePublic(BrowserOptions, [
     'addBluetoothDevice',
     'deleteCurrentProfile',
     'enableCertificateButton',
     'enableFactoryResetSection',
     'getCurrentProfile',
     'getStartStopSyncButton',
@@ skipping 84 matching lines @@
       }
       button.textContent = loadTimeData.getString(strId);
     };
   }
 
   // Export
   return {
     BrowserOptions: BrowserOptions
   };
 });