MD Settings: Fix runtime error when visiting "manage passwords" page.

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' shows a subpage beneath a subheader. The header contains
  * the subpage title and a back icon. The back icon fires an event which
  * is caught by settings-animated-pages, so it requires no separate handling.
  */
 
 Polymer({
   is: 'settings-subpage-search',
 
   behaviors: [CrSearchFieldBehavior],
 
+  /** @return {!HTMLInputElement} */
+  getSearchInput: function() {
+    return this.$.searchInput;
+  },
+
   /** @private */
   onTapClear_: function() {
     this.setValue('');
   },
 });