Improve document.appendText test as follow up to "Fix Try Dart newline handling on IE11" change.

tests/html/element_add_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file
 
 library ElementAddTest;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'util.dart';
 import 'dart:html';
 
@@ skipping 66 matching lines @@
     test('htmlelement', () {
       var el = new DivElement();
       var twoNewLines = "\n\n";
       el.appendText(twoNewLines);
       // No children were created.
       expect(el.children.length, equals(0));
       // One text node was added.
       expect(el.nodes.length, equals(1));
       expect(el.nodes[0], isText);
       expect(el.nodes[0].text, equals(twoNewLines));
+      expect(el.text, equals(twoNewLines));
     });
 
     test('documentFragment', () {
       var fragment = new DocumentFragment();
       fragment.appendText('foo');
       // No children were created.
       expect(fragment.children.length, equals(0));
       // One text node was added.
       expect(fragment.nodes.length, equals(1));
     });
@@ skipping 134 matching lines @@
       var child = new DivElement();
       parent.children.add(child);
 
       parent.insertAdjacentText('beforeend', 'test');
 
       expect(parent.nodes.length, 2);
       expect(parent.nodes[1], isText);
     });
   });
 }