MD Bookmarks: Initial screenreader accessibility improvements

chrome/test/data/webui/md_bookmarks/toast_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-toast-manager>', function() {
   var toastManager;
   var store;
 
   setup(function() {
     toastManager = document.createElement('bookmarks-toast-manager');
     replaceBody(toastManager);
   });
 
   test('simple show/hide', function() {
     toastManager.show('test', false);
     assertTrue(toastManager.open_);
     assertEquals('test', toastManager.$.content.textContent);
     assertTrue(toastManager.$$('paper-button').hidden);
 
     toastManager.hide();
     assertFalse(toastManager.open_);
 
     toastManager.show('test', true);
     assertFalse(toastManager.$$('paper-button').hidden);
+
+    toastManager.hide();
+    assertTrue(toastManager.$.button.hidden);
   });
 
   test('auto hide', function() {
     var timerProxy = new bookmarks.TestTimerProxy();
     timerProxy.immediatelyResolveTimeouts = false;
     toastManager.timerProxy_ = timerProxy;
 
     toastManager.duration = 100;
 
     toastManager.show('test', false);
     assertEquals(0, toastManager.hideTimeoutId_);
     assertTrue(toastManager.open_);
 
     timerProxy.runTimeoutFn(0);
     assertEquals(null, toastManager.hideTimeoutId_);
     assertFalse(toastManager.open_);
 
     // Check that multiple shows reset the timeout.
     toastManager.show('test', false);
     assertEquals(1, toastManager.hideTimeoutId_);
     assertTrue(toastManager.open_);
 
     toastManager.show('test2', false);
     assertFalse(timerProxy.hasTimeout(1));
     assertEquals(2, toastManager.hideTimeoutId_);
     assertTrue(toastManager.open_);
   });
 });