Fix inconsistency with null vs undefined in dart:js

tests/lib/js/null_test.dart

Index: tests/lib/js/null_test.dart
diff --git a/pkg/web_components/test/location_wrapper_test.dart b/tests/lib/js/null_test.dart
similarity index 65%
copy from pkg/web_components/test/location_wrapper_test.dart
copy to tests/lib/js/null_test.dart
index a1c531ad50b6d1fa0737f10aa73ee0533142899d..82bc9df534a559bc24022b9f603641e7cb7a0209 100644
--- a/pkg/web_components/test/location_wrapper_test.dart
+++ b/tests/lib/js/null_test.dart
@@ -2,16 +2,16 @@
 // 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 template_wrappers_test;
+library null_test;
 
-import 'dart:html';
-import 'package:unittest/html_config.dart';
+import 'dart:js';
 import 'package:unittest/unittest.dart';
+import 'package:unittest/html_config.dart';
 
 main() {
   useHtmlConfiguration();
-
-  test('OK to access location with platform.js', () {
-    expect(window.location.toString(), window.location.href);
+  test('null is sent as null', () {
+    expect(context['isNull'].apply([null]), isTrue);
+    expect(context['isUndefined'].apply([null]), isFalse);
   });
 }