MD History: Add shortcuts for 'Delete' and 'Backspace' to delete selected items

chrome/browser/resources/md_history/history_list.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-list',
 
   properties: {
     // The search term for the current query. Set when the query returns.
     searchedTerm: {
@@ skipping 188 matching lines @@
     });
     md_history.BrowserService.getInstance()
         .deleteItems(toBeRemoved)
         .then(function(items) {
           this.removeDeletedHistory_(items);
           this.fire('unselect-all');
         }.bind(this));
   },
 
   /**
+   * Return the number of history items to be deleted.
+   * @return {number}
+   */
+  numToBeDeleted: function() {

[tsergeant, 2016/07/19 05:09:41]

Nit: Rename this to something like numSelected or selectedCount, since that's
what you're actually counting here.

[lshang, 2016/07/20 01:19:09]

I deleted this method and used 'toolbar.count' instead, but I'll pay attention
to method's names next time. Good suggestion.

+    return this.historyData_.filter(function(item) {
+      return item.selected;
+    }).length;
+  },
+
+  /**
    * Called when the page is scrolled to near the bottom of the list.
    * @private
    */
   loadMoreData_: function() {
     if (this.resultLoadingDisabled_ || this.querying)
       return;
 
     this.fire('load-more-history');
   },
 
@@ skipping 56 matching lines @@
 
   /**
    * @param {number} index
    * @return {boolean}
    * @private
    */
   isFirstItem_: function(index) {
     return index == 0;
   }
 });