Reapply DOMFormData => FormData rename. (this time with a fix for Dartium)

tests/html/form_data_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('FormDataTest');
 
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
@@ skipping 16 matching lines @@
 
   test('appendTest', () {
     var form = new FormData();
     form.append('test', '1', 'foo');
     form.append('username', 'Elmo', 'foo');
     form.append('address', '1 Sesame Street', 'foo');
     form.append('password', '123456', 'foo');
     expect(form, isNotNull);
   });
 }