Disable wallpaper button in Guest mode settings

chrome/browser/resources/options/browser_options.js

Index: chrome/browser/resources/options/browser_options.js
diff --git a/chrome/browser/resources/options/browser_options.js b/chrome/browser/resources/options/browser_options.js
index 1bc711f8e33eaccc7c1fde4d77f5493a1b866c1f..a373375126df5593bbcf12fe1710ae90041e1d79 100644
--- a/chrome/browser/resources/options/browser_options.js
+++ b/chrome/browser/resources/options/browser_options.js
@@ -1492,8 +1492,7 @@ cr.define('options', function() {
      * @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.
@@ -1939,6 +1938,19 @@ cr.define('options', function() {
     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.