Add a SigninAllowed policy.

chrome/browser/resources/options/browser_options.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() {
   var OptionsPage = options.OptionsPage;
   var ArrayDataModel = cr.ui.ArrayDataModel;
   var RepeatingButton = cr.ui.RepeatingButton;
 
   //
@@ skipping 646 matching lines @@
         expander.textContent = loadTimeData.getString('hideAdvancedSettings');
     },
 
     /**
      * Updates the sync section with the given state.
      * @param {Object} syncData A bunch of data records that describe the status
      *     of the sync system.
      * @private
      */
     updateSyncState_: function(syncData) {
-      if (!syncData.syncSystemEnabled) {
+      if (!syncData.syncSystemEnabled || !syncData.signinAllowed) {
         $('sync-section').hidden = true;
         return;
       }
 
       $('sync-section').hidden = false;
       this.signedIn = syncData.signedIn;
       // Display the "setup sync" button if we're signed in and sync is not
       // managed.
       $('customize-sync').hidden = !(syncData.signedIn && !syncData.managed);
 
@@ skipping 703 matching lines @@
     BrowserOptions.getLoggedInUsername = function() {
       return BrowserOptions.getInstance().username_;
     };
   }
 
   // Export
   return {
     BrowserOptions: BrowserOptions
   };
 });