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

chrome/browser/resources/md_history/app.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.
 
 Polymer({
   is: 'history-app',
 
   properties: {
     // The id of the currently selected page.
     selectedPage_: {type: String, value: 'history', observer: 'unselectAll'},
@@ skipping 117 matching lines @@
     e = /** @type {cr.ui.CanExecuteEvent} */(e);
     switch (e.command.id) {
       case 'find-command':
         e.canExecute = true;
         break;
       case 'slash-command':
         e.canExecute =
             !(this.$.toolbar.searchBar.showingSearch &&
               this.$.toolbar.searchBar.isSearchFocused());
         break;
+      case 'delete-command':
+        e.canExecute = this.$.toolbar.count > 0;
+        break;
     }
   },
 
   /**
    * @param {Event} e
    * @private
    */
   onCommand_: function(e) {
     if (e.command.id == 'find-command' || e.command.id == 'slash-command')
       this.$.toolbar.showSearchField();
+    if (e.command.id == 'delete-command')
+      this.deleteSelected();
   },
 
   /**
    * @param {!Array<!ForeignSession>} sessionList Array of objects describing
    *     the sessions from other devices.
    * @param {boolean} isTabSyncEnabled Is tab sync enabled for this profile?
    */
   setForeignSessions: function(sessionList, isTabSyncEnabled) {
     if (!isTabSyncEnabled)
       return;
@@ skipping 26 matching lines @@
    * @param {boolean} incremental
    * @param {string} searchTerm
    * @return {boolean} Whether a loading spinner should be shown (implies the
    *     backend is querying a new search term).
    * @private
    */
   shouldShowSpinner_: function(querying, incremental, searchTerm) {
     return querying && !incremental && searchTerm != '';
   },
 });