[MD History] Make forward/backward work in grouped mode.

chrome/browser/resources/md_history/grouped_list.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 {{domain: string,
  *            visits: !Array<HistoryEntry>,
  *            rendered: boolean,
  *            expanded: boolean}}
  */
@@ skipping 64 matching lines @@
       domains[domainIndexes[domain]].visits.push(visit);
     }
     var sortByVisits = function(a, b) {
       return b.visits.length - a.visits.length;
     };
     domains.sort(sortByVisits);
 
     return domains;
   },
 
+  /** @private */
   updateGroupedHistoryData_: function() {
     if (this.historyData.length == 0) {
       this.groupedHistoryData_ = [];
       return;
     }
 
     if (this.range == HistoryRange.WEEK) {
       // Group each day into a list of results.
       var days = [];
       var currentDayVisits = [this.historyData[0]];
@@ skipping 86 matching lines @@
 
   /**
    * @param {boolean} expanded
    * @return {string}
    * @private
    */
   getDropdownIcon_: function(expanded) {
     return expanded ? 'cr:expand-less' : 'cr:expand-more';
   },
 });