use .append instead of .nodes.add

tests/html/documentfragment_test.dart

 // Copyright (c) 2011, 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 DocumentFragmentTest;
 import "package:expect/expect.dart";
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'util.dart';
 import 'dart:html';
@@ skipping 143 matching lines @@
 
     test('setting children overwrites nodes as well', () {
       init();
       fragment.children = [new Element.tag("DIV"), new Element.tag("HEAD")];
       expect(_nodeStrings(fragment.nodes), equals(["DIV", "HEAD"]));
     });
   });
 
   test('setting innerHtml works', () {
     var fragment = new DocumentFragment();
-    fragment.nodes.add(new Text("foo"));
+    fragment.append(new Text("foo"));
     fragment.innerHtml = "<a>bar</a>baz";
     expect(_nodeStrings(fragment.nodes), equals(["A", "baz"]));
   });
 
   test('getting innerHtml works', () {
     var fragment = new DocumentFragment();
     fragment.nodes.addAll([new Text("foo"), new Element.html("<A>bar</A>")]);
     expect(fragment.innerHtml, "foo<a>bar</a>");
   });
 
   test('query searches the fragment', () {
     var fragment = new DocumentFragment.html(
       "<div class='foo'><a>foo</a><b>bar</b></div>");
     expect(fragment.query(".foo a").tagName, "A");
     expect(_nodeStrings(fragment.queryAll(".foo *")), equals(["A", "B"]));
   });
 }