Make the user manager UI not permit guest mode when preferences dictate

chrome/browser/resources/user_manager/user_manager.js

 // Copyright 2013 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.
 <include src="../../../../ui/login/screen.js">
 <include src="../../../../ui/login/bubble.js">
 <include src="../../../../ui/login/login_ui_tools.js">
 <include src="../../../../ui/login/display_manager.js">
 <include src="control_bar.js">
 <include src="../../../../ui/login/account_picker/screen_account_picker.js">
 <include src="../../../../ui/login/account_picker/user_pod_row.js">
@@ skipping 16 matching lines @@
   cr.addSingletonGetter(Oobe);
 
   Oobe.prototype = {
     __proto__: DisplayManager.prototype,
   };
 
   /**
    * Shows the given screen.
    * @param {Object} screen Screen params dict, e.g. {id: screenId, data: data}
    */
-  Oobe.showUserManagerScreen = function() {
+  Oobe.showUserManagerScreen = function(showGuest) {
     Oobe.getInstance().showScreen({id: 'account-picker',
                                    data: {disableAddUser: false}});
     // The ChromeOS account-picker will hide the AddUser button if a user is
     // logged in and the screen is "locked", so we must re-enabled it
     $('add-user-header-bar-item').hidden = false;
 
+    // Hide the Guest Mode option if the user is not permitted to select it.
+    $('guest-user-button').hidden = !showGuest;
+    $('login-header-bar').hidden = false;
+
     // Disable the context menu, as the Print/Inspect element items don't
     // make sense when displayed as a widget.
     document.addEventListener('contextmenu', function(e) {e.preventDefault();});
 
     var hash = window.location.hash;
     if (hash && hash == '#tutorial')
       UserManagerTutorial.startTutorial();
   };
 
   /**
@@ skipping 69 matching lines @@
 
 cr.define('UserManager', function() {
   'use strict';
 
   function initialize() {
     cr.ui.login.DisplayManager.initialize();
     cr.ui.login.UserManagerTutorial.initialize();
     login.AccountPickerScreen.register();
     cr.ui.Bubble.decorate($('bubble'));
     login.HeaderBar.decorate($('login-header-bar'));
+
+    // Hide the header bar until the showUserManagerMethod can apply function
+    // parameters that affect widget visiblity.
+    $('login-header-bar').hidden = true;
     chrome.send('userManagerInitialize');
   }
 
   // Return an object with all of the exports.
   return {
     initialize: initialize
   };
 });
 
 var Oobe = cr.ui.Oobe;
 
 // Allow selection events on components with editable text (password field)
 // bug (http://code.google.com/p/chromium/issues/detail?id=125863)
 disableTextSelectAndDrag(function(e) {
   var src = e.target;
   return src instanceof HTMLTextAreaElement ||
          src instanceof HTMLInputElement &&
          /text|password|search/.test(src.type);
 });
 
 document.addEventListener('DOMContentLoaded', UserManager.initialize);