[MD Bookmarks] Add toasts.

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 25 matching lines @@
           createFolder(
               '2',
               [
                 createFolder('21', []),
               ]))
     });
     store.replaceSingleton();
 
     commandManager = new TestCommandManager();
     replaceBody(commandManager);
+    document.body.appendChild(
+        document.createElement('bookmarks-toast-manager'));
 
     Polymer.dom.flush();
   });
 
   test('can only copy single URL items', function() {
     assertFalse(commandManager.canExecute(Command.COPY, new Set(['11'])));
     assertFalse(commandManager.canExecute(Command.COPY, new Set(['11', '13'])));
     assertTrue(commandManager.canExecute(Command.COPY, new Set(['13'])));
   });
 
@@ skipping 200 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/']);
   });
 });