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

chrome/browser/resources/md_history/side_bar.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.
 
 Polymer({
   is: 'history-side-bar',
 
   properties: {
     selectedPage: {
       type: String,
       notify: true
-    }
+    },
+
+    showFooter: Boolean,
   },
 
   /**
    * Handles menu selection changes.
    * @param {Event} e
    * @private
    */
   onSelect_: function(e) {
     this.fire('unselect-all');
     this.selectedPage = e.detail.item.getAttribute('view-id');
   },
 
   /**
    * Relocates the user to the clear browsing data section of the settings page.
    * @private
    */
   onClearBrowsingDataTap_: function() {
     window.location.href = 'chrome://settings/clearBrowserData';
   },
 });