[MD History] Factor out a common HistoryListBehavior.

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.
 
 cr.define('md_history', function() {
   var HistoryItem = Polymer({
     is: 'history-item',
 
     properties: {
       // Underlying HistoryEntry data for this item. Contains read-only fields
@@ skipping 13 matching lines @@
       isCardStart: {type: Boolean, reflectToAttribute: true},
 
       isCardEnd: {type: Boolean, reflectToAttribute: true},
 
       // True if the item is being displayed embedded in another element and
       // should not manage its own borders or size.
       embedded: {type: Boolean, reflectToAttribute: true},
 
       hasTimeGap: {type: Boolean},
 
-      numberOfItems: {type: Number}
+      numberOfItems: {type: Number},
+
+      // The path of this history item inside its parent.
+      path: String,
     },
 
     /**
      * When a history-item is selected the toolbar is notified and increases
      * or decreases its count of selected items accordingly.
      * @private
      */
     onCheckboxSelected_: function() {
+      // TODO(calamity): Fire this event whenever |selected| changes.
       this.fire('history-checkbox-select', {
+        element: this,
         countAddition: this.$.checkbox.checked ? 1 : -1
       });
     },
 
     /**
      * Remove bookmark of current item when bookmark-star is clicked.
      * @private
      */
     onRemoveBookmarkTap_: function() {
       if (this.$['bookmark-star'] == this.root.activeElement)
@@ skipping 77 matching lines @@
 
     if (searchedTerm)
       return currentItem.dateShort != nextItem.dateShort;
 
     return currentItem.time - nextItem.time > BROWSING_GAP_TIME &&
         currentItem.dateRelativeDay == nextItem.dateRelativeDay;
   };
 
   return { HistoryItem: HistoryItem };
 });