Add a lock to the managed user settings page and require authentication for unlocking.

chrome/browser/resources/options/managed_user_settings.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.
 
 if (loadTimeData.getBoolean('managedUsersEnabled')) {
 
 cr.define('options', function() {
   /** @const */ var OptionsPage = options.OptionsPage;
 
   //////////////////////////////////////////////////////////////////////////////
@@ skipping 28 matching lines @@
 
       $('get-content-packs-button').onclick = function(event) {
         window.open(loadTimeData.getString('getContentPacksURL'));
       };
 
       $('managed-user-settings-confirm').onclick = function() {
         OptionsPage.closeOverlay();
       };
 
       $('set-passphrase').onclick = function() {
-        // TODO(bauerb): Set passphrase
+        OptionsPage.navigateToPage('setPassphrase');
       };
     },
   };
 
    // Export
   return {
     ManagedUserSettings: ManagedUserSettings
   };
 });
 
 }