TaskManager: minor UI cleanup (consume Esc with context menu opened, use classList).

chrome/browser/resources/shared/js/cr/ui/context_menu_handler.js

 // Copyright (c) 2011 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('cr.ui', function() {
 
   const Menu = cr.ui.Menu;
 
   /**
    * Handles context menus.
@@ skipping 114 matching lines @@
         case 'mousedown':
           if (!this.menu.contains(e.target))
             this.hideMenu();
           else
             e.preventDefault();
           break;
         case 'keydown':
           // keyIdentifier does not report 'Esc' correctly
           if (e.keyCode == 27 /* Esc */) {
             this.hideMenu();
+            e.stopPropagation();
+            e.preventDefault();
 
           // If the menu is visible we let it handle all the keyboard events.
           } else if (this.menu) {
             this.menu.handleKeyDown(e);
             e.preventDefault();
             e.stopPropagation();
           }
           break;
 
         case 'activate':
@@ skipping 71 matching lines @@
    * The singleton context menu handler.
    * @type {!ContextMenuHandler}
    */
   var contextMenuHandler = new ContextMenuHandler;
 
   // Export
   return {
     contextMenuHandler: contextMenuHandler
   };
 });