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,
   },
 
   toggle: function() {
     this.$.drawer.toggle();
   },
 
   /** @private */
   onDrawerFocus_: function() {
     // The desired behavior is for the app-drawer to focus the currently
     // selected menu item on opening. However, it will always focus the first
     // focusable child. Therefore, we set tabindex=0 on the app-drawer so that
     // it will focus itself and then immediately delegate focus to the selected
     // item in this listener.
     this.$.menu.selectedItem.focus();
   },
 
   /** @private */
   onSelectorActivate_: function() {
     this.$.drawer.close();
   },
 
   /**
    * Relocates the user to the clear browsing data section of the settings page.
    * @private
    */
   onClearBrowsingDataTap_: function() {
     window.location.href = 'chrome://settings/clearBrowserData';
   },
 });