MD Settings: Fix rendering of popup menus inside iron-lists.

chrome/browser/resources/settings/search_engines_page/omnibox_extension_entry.js

 // Copyright 2016 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 'settings-omnibox-extension-entry' is a component for showing
  * an omnibox extension with its name and keyword.
  */
 Polymer({
   is: 'settings-omnibox-extension-entry',
 
+  behaviors: [settings.ListItemBehavior],
+
   properties: {
     /** @type {!SearchEngine} */
     engine: Object,
 
     /** @private {!settings.SearchEnginesBrowserProxy} */
     browserProxy_: Object,
   },
 
   /** @override */
   created: function() {
@@ skipping 19 matching lines @@
 
   /**
    * @param {string} url
    * @return {string} A set of icon URLs.
    * @private
    */
   getIconSet_: function(url) {
     return cr.icon.getFavicon(url);
   },
 });