MD History: Use computed functions for card borders and time gaps

chrome/browser/resources/md_history/history_item.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-item',
 
   properties: {
     // Underlying HistoryEntry data for this item. Contains read-only fields
     // from the history backend, as well as fields computed by history-list.
@@ skipping 26 matching lines @@
       value: false,
       reflectToAttribute: true
     },
 
     isCardEnd: {
       type: Boolean,
       value: false,
       reflectToAttribute: true
     },
 
+    hasTimeGap: {
+      type: Boolean,
+      value: false,
+    },
+
     numberOfItems: {
       type: Number,
       value: 0
     }
   },
 
   observers: [
     'setSearchedTextToBold_(item.title, searchTerm)'
   ],
 
@@ skipping 80 matching lines @@
    */
   cardTitle_: function(numberOfItems, historyDate, search) {
     if (!search)
       return this.item.dateRelativeDay;
 
     var resultId = numberOfItems == 1 ? 'searchResult' : 'searchResults';
     return loadTimeData.getStringF('foundSearchResults', numberOfItems,
         loadTimeData.getString(resultId), search);
   }
 });