ChromeOS OOBE: make "System Security Settings" popup dialog backgroung gray.

chrome/browser/resources/chromeos/login/oobe.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.
 
 /**
  * @fileoverview Out of the box experience flow (OOBE).
  * This is the main code for the OOBE WebUI implementation.
  */
 
 // <include src="login_shared.js">
@@ skipping 315 matching lines @@
     },
 
     /**
      * This method takes care of switching to material-design OOBE.
      * @private
      */
     setMDMode_: function() {
       if (loadTimeData.getString('newOobeUI') == 'on') {
         $('oobe').setAttribute('md-mode', 'true');
         $('oobe-shield').setAttribute('md-mode', 'true');
+        $('popup-overlay').setAttribute('md-mode', 'true');
       } else {
         $('oobe').removeAttribute('md-mode');
         $('oobe-shield').removeAttribute('md-mode');
+        $('popup-overlay').removeAttribute('md-mode');
       }
     },
   };
 });