MD Settings: Allow searching the languages list in "add language" dialog.

chrome/browser/resources/settings/settings_page/settings_subpage_search.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-subpage-search' shows a search field in the subpage's header.
  */
 
 Polymer({
   is: 'settings-subpage-search',
 
   behaviors: [CrSearchFieldBehavior],
 
+  properties: {
+    autofocus: Boolean,
+  },
+
   /** @return {!HTMLInputElement} */
   getSearchInput: function() {
     return this.$.searchInput;
   },
 
   /** @private */
   onTapClear_: function() {
     this.setValue('');
   },
 });