Remove uses of unittest in the HTML tests where possible.

pkg/dev_compiler/test/codegen/lib/html/non_instantiated_is_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.
 
 // Regression test for dart2js, that used to emit wrong code on is
 // checks of native classes that are not instantiated.
 
 import 'dart:html';
-import 'package:unittest/unittest.dart';
-import 'package:unittest/html_config.dart';
+
+import 'package:expect/expect.dart';
 
 var a = [new Object()];
 
 main() {
-  useHtmlConfiguration();
-
-  test('is', () {
-    expect(a[0] is Node, isFalse);
-  });
+  Expect.isFalse(a[0] is Node);
 }