MD Settings: Restore Search engines table headers.

chrome/browser/resources/settings/search_engines_page/search_engines_list.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-engines-list' is a component for showing a
  * list of search engines.
  */
 Polymer({
   is: 'settings-search-engines-list',
 
   behaviors: [settings.GlobalScrollTargetBehavior],
 
   properties: {
     /** @type {!Array<!SearchEngine>} */
     engines: Array,
 
     /** @override */
     subpageRoute: {
       type: Object,
       value: settings.Route.SEARCH_ENGINES,
     },
+
+    /** Whether column headers should be displayed */
+    hideHeaders: Boolean,
   },
 });