Add all dart:html tests from the sdk to test/codegen.

test/codegen/lib/html/util.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 test.html.util;
+
+import 'dart:html';
+import 'package:unittest/unittest.dart';
+
+void expectUnsupported(f) => expect(f, throwsUnsupportedError);
+
+void expectEmptyRect(ClientRect rect) {
+  expect(rect.bottom, isZero);
+  expect(rect.top, isZero);
+  expect(rect.left, isZero);
+  expect(rect.right, isZero);
+  expect(rect.height, isZero);
+  expect(rect.width, isZero);
+}