Fixing CharacterData.remove not working on FireFox.

tests/html/cdata_test.dart

+// Copyright (c) 2013, 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 cdata_test;
+import '../../pkg/unittest/lib/unittest.dart';
+import '../../pkg/unittest/lib/html_config.dart';
+import 'dart:html';
+
+
+main() {
+  test('remove', () {
+    var div = new Element.html('<div>content</div>');
+    var cdata = div.nodes[0];
+    expect(cdata is CharacterData, true);
+    expect(cdata, isNotNull);
+    expect(div.innerHtml, 'content');
+
+    cdata.remove();
+    expect(div.innerHtml, '');
+  });
+}