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

chrome/browser/resources/md_history/list_container.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-list-container',
 
   properties: {
     // The path of the currently selected page.
     selectedPage_: String,
@@ skipping 76 matching lines @@
    * Delete all the currently selected history items. Will prompt the user with
    * a dialog to confirm that the deletion should be performed.
    */
   deleteSelectedWithPrompt: function() {
     if (!loadTimeData.getBoolean('allowDeletingHistory'))
       return;
 
     this.$.dialog.open();
   },
 
+  /** @return {HistoryListElement} */
+  getHistoryList: function() {
+    return this.$['infinite-list'];
+  },
+
   /**
    * @param {string} searchTerm
    * @private
    */
   searchTermChanged_: function(searchTerm) { this.queryHistory(false); },
 
   /**
    * @param {HistoryRange} range
    * @private
    */
@@ skipping 35 matching lines @@
   onDialogConfirmTap_: function() {
     this.$['infinite-list'].deleteSelected();
     this.$.dialog.close();
   },
 
   /** @private */
   onDialogCancelTap_: function() {
     this.$.dialog.close();
   }
 });