Disable modifying extensions when in managed mode.

chrome/browser/resources/options2/options_page.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.define('options', function() {
   /////////////////////////////////////////////////////////////////////////////
   // OptionsPage class:
 
   /**
    * Base class for options page.
@@ skipping 690 matching lines @@
           controlledByPolicy = true;
         else if (inputElements[i].controlledBy == 'extension')
           controlledByExtension = true;
       }
 
       if (!controlledByPolicy && !controlledByExtension) {
         this.pageDiv.classList.remove('showing-banner');
       } else {
         this.pageDiv.classList.add('showing-banner');
 
-        var text = bannerDiv.querySelector('.managed-prefs-text');
+        var text = bannerDiv.querySelector('#managed-prefs-text');
         if (controlledByPolicy && !controlledByExtension) {
           text.textContent =
               loadTimeData.getString('policyManagedPrefsBannerText');
         } else if (!controlledByPolicy && controlledByExtension) {
           text.textContent =
               loadTimeData.getString('extensionManagedPrefsBannerText');
         } else if (controlledByPolicy && controlledByExtension) {
           text.textContent = loadTimeData.getString(
               'policyAndExtensionManagedPrefsBannerText');
         }
@@ skipping 175 matching lines @@
     canShowPage: function() {
       return true;
     },
   };
 
   // Export
   return {
     OptionsPage: OptionsPage
   };
 });