Adding support checks for partially supported element types and updating tests.

tests/html/contentelement_test.dart

Index: tests/html/contentelement_test.dart
diff --git a/tests/html/contentelement_test.dart b/tests/html/contentelement_test.dart
deleted file mode 100644
index b7911ebc188daacfdbfe995ce85db26aa736c13e..0000000000000000000000000000000000000000
--- a/tests/html/contentelement_test.dart
+++ /dev/null
@@ -1,20 +0,0 @@
-// 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 contentelement_test;
-import '../../pkg/unittest/lib/unittest.dart';
-import '../../pkg/unittest/lib/html_config.dart';
-import 'dart:html';
-
-main() {
-  useHtmlConfiguration();
-
-  var isContentElement =
-      predicate((x) => x is ContentElement, 'is a ContentElement');
-
-  test('constructor', () {
-      var e = new ContentElement();
-      expect(e, isContentElement);
-    });
-}