[MD History] Add keyboard navigation to the main history list.

chrome/browser/resources/md_history/history_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.
 
 Polymer({
   is: 'history-list',
 
   behaviors: [HistoryListBehavior],
 
   properties: {
     // The search term for the current query. Set when the query returns.
     searchedTerm: {
       type: String,
       value: '',
     },
 
     querying: Boolean,
 
     // An array of history entries in reverse chronological order.
     historyData_: Array,
 
     resultLoadingDisabled_: {
       type: Boolean,
       value: false,
     },
+
+    lastFocused_: Object,
   },
 
   listeners: {
     'scroll': 'notifyListScroll_',
     'remove-bookmark-stars': 'removeBookmarkStars_',
   },
 
   /** @override */
   attached: function() {
     // It is possible (eg, when middle clicking the reload button) for all other
@@ skipping 134 matching lines @@
 
   /**
    * @param {number} index
    * @return {string}
    * @private
    */
   pathForItem_: function(index) {
     return 'historyData_.' + index;
   },
 });