MD History: Delete button in the toolbar allows deletion of multiple history-items.

chrome/browser/resources/md_history/history_card.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-card',
 
   properties: {
     // The date of these history items.
     historyDate: {
       type: String,
       value: ''
     },
     // The list of history results that were accessed for a particular day in
     // reverse chronological order.
     historyItems: {
       type: Array,
       value: function() { return []; }
     }
   },
 
   /**
    * Check whether the time difference between the given historyItem and the
    * next one is large enough for a spacer to be required.
    * @param {number} index The index number of the first item being compared.
+   * @param {number} itemsLength The number of items on the card. Used to force
+   * needsTimeGap_ to run for every item if an item is deleted from the card.
    * @return {boolean} Whether or not time gap separator is required.
    * @private
    */
-  needsTimeGap_: function(index) {
+  needsTimeGap_: function(index, itemsLength) {
     var items = this.historyItems;
     return index + 1 < items.length &&
         items[index].time - items[index + 1].time > BROWSING_GAP_TIME;
   }
 });