Copy lib/dom tests that use dart:html to lib/html.

tests/html/window_mangling_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('WindowManglingTest');
 #import('../../lib/unittest/unittest.dart');
 #import('../../lib/unittest/html_config.dart');
 #import('dart:html', prefix: 'dom');
 
 // Defined in dom.Window.
@@ skipping 15 matching lines @@
   test('windowEquals', () {
       Expect.isFalse($eq(win, win));
       Expect.isTrue(win == win);
     });
 
   test('windowEquals', () {
       Expect.isFalse($eq$(win, win));
       Expect.isTrue(win == win);
     });
 }