Add a footer about other forms of history to the MD history page.

chrome/browser/resources/md_history/app.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.
 
 /**
  * @typedef {{querying: boolean,
  *            searchTerm: string,
  *            results: ?Array<!HistoryEntry>,
  *            info: ?HistoryQuery,
  *            incremental: boolean,
  *            range: HistoryRange,
  *            groupedOffset: number,
  *            sessionList: ?Array<!ForeignSession>}}
  */
 var QueryState;
 
 Polymer({
   is: 'history-app',
 
   properties: {
+    // Whether to display the footer.
+    showFooter: Boolean,
+
     // The id of the currently selected page.
     selectedPage_: String,
 
     // Whether domain-grouped history is enabled.
     grouped_: {
       type: Boolean,
       reflectToAttribute: true
     },
 
     // Whether the first set of results have returned.
@@ skipping 218 matching lines @@
    * @param {boolean} incremental
    * @param {string} searchTerm
    * @return {boolean} Whether a loading spinner should be shown (implies the
    *     backend is querying a new search term).
    * @private
    */
   shouldShowSpinner_: function(querying, incremental, searchTerm) {
     return querying && !incremental && searchTerm != '';
   }
 });