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

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

 // Copyright 2015 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-search-engine-entry' is a component for showing a
  * search engine with its name, domain and query URL.
  */
 Polymer({
   is: 'settings-search-engine-entry',
 
+  behaviors: [ListItemBehavior],
+
   properties: {
     /** @type {!SearchEngine} */
     engine: Object,
 
     /** @private {boolean} */
     showEditSearchEngineDialog_: Boolean,
 
     /** @type {boolean} */
     isDefault: {
       reflectToAttribute: true,
@@ skipping 53 matching lines @@
   /**
    * @param {?string} url The icon URL if available.
    * @return {string} A set of icon URLs.
    * @private
    */
   getIconSet_: function(url) {
     // Force default icon, if no |engine.iconURL| is available.
     return cr.icon.getFavicon(url || '');
   },
 });