[MD Bookmarks] Make disabled buttons in context menu do nothing when clicked.

chrome/test/data/webui/md_bookmarks/command_manager_test.js

 // Copyright 2017 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.
 
 suite('<bookmarks-command-manager>', function() {
   var commandManager;
   var store;
   var lastCommand;
   var lastCommandIds;
 
@@ skipping 246 matching lines @@
     // No divider line should be visible when only 'Open' commands are enabled.
     commandManager.openCommandMenuAtPosition(0, 0);
     commandManager.root.querySelectorAll('hr').forEach(element => {
       assertTrue(element.hidden);
     });
   });
 
   test('cannot edit unmodifiable nodes', function() {
     // Cannot edit root folders.
     var items = new Set(['1']);
+    store.data.selection.items = items;
     assertFalse(commandManager.canExecute(Command.EDIT, items));
     assertFalse(commandManager.canExecute(Command.DELETE, items));
 
     store.data.nodes['12'].unmodifiable = 'managed';
     store.notifyObservers();
 
     items = new Set(['12']);
     assertFalse(commandManager.canExecute(Command.EDIT, items));
     assertFalse(commandManager.canExecute(Command.DELETE, items));
+
+    commandManager.openCommandMenuAtPosition(0, 0);
+    var commandItem = {};
+    commandManager.root.querySelectorAll('.dropdown-item').forEach(element => {
+      commandItem[element.getAttribute('command')] = element;
+    });
+    MockInteractions.tap(commandItem[Command.EDIT]);
+    commandManager.assertLastCommand(null);
   });
 });
 
 suite('<bookmarks-item> CommandManager integration', function() {
   var list;
   var items;
   var commandManager;
   var openedTabs;
 
   setup(function() {
@@ skipping 59 matching lines @@
     assertOpenedTabs(['http://111/', 'http://12/']);
   });
 
   test('control-double click opens full selection', function() {
     customClick(items[0]);
     simulateDoubleClick(items[2], {ctrlKey: true});
 
     assertOpenedTabs(['http://111/', 'http://13/']);
   });
 });