Disable chrome://options UI elements if the corresponding preference is not user-modifiable.

chrome/browser/resources/options/pref_ui.js

 // Copyright (c) 2011 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('options', function() {
 
   var Preferences = options.Preferences;
 
   /**
    * Helper function update element's state from pref change event.
    * @private
    * @param {!HTMLElement} el The element to update.
    * @param {!Event} event The pref change event.
    */
   function updateElementState_(el, event) {
-    el.managed = event.value && event.value['managed'] != undefined ?
-        event.value['managed'] : false;
+    el.managed = false;
 
-    // Managed UI elements can only be disabled as a result of being
-    // managed. They cannot be enabled as a result of a pref being
-    // unmanaged.
-    if (el.managed)
-      el.disabled = true;
+    if (!event.value)
+      return;
 
-    // Disable UI elements if backend says so.
-    if (!el.disabled && event.value && event.value['disabled'])
-      el.disabled = true;
+    el.managed = event.value['managed'];
+
+    // Disable UI elements if the backend says so.
+    // |reenable| is a flag that tells us if the element is disabled because the
+    // preference is not modifiable by the user. If the element is disabled but
+    // the flag is not set, it means that the element has been disabled
+    // somewhere else, so we don't do anything.
+    if (el.disabled && !el.notUserModifiable)
+      return;
+
+    el.disabled = event.value['disabled'];
+    el.notUserModifiable = event.value['disabled'];
   }
 
   /////////////////////////////////////////////////////////////////////////////
   // PrefCheckbox class:
   // TODO(jhawkins): Refactor all this copy-pasted code!
 
   // Define a constructor that uses an input element as its underlying element.
   var PrefCheckbox = cr.ui.define('input');
 
   PrefCheckbox.prototype = {
@@ skipping 483 matching lines @@
     PrefCheckbox: PrefCheckbox,
     PrefNumber: PrefNumber,
     PrefNumeric: PrefNumeric,
     PrefRadio: PrefRadio,
     PrefRange: PrefRange,
     PrefSelect: PrefSelect,
     PrefTextField: PrefTextField
   };
 
 });