Fix js/null_test to run also in CSP mode

tests/lib/js/null_test.js

Index: tests/lib/js/null_test.js
diff --git a/pkg/collection/lib/src/utils.dart b/tests/lib/js/null_test.js
similarity index 56%
copy from pkg/collection/lib/src/utils.dart
copy to tests/lib/js/null_test.js
index c9c753777f07c1c5bd930fa4a3a7e32a5377db0f..35e1241982aceb49c5042bf87e4885141fe30f26 100644
--- a/pkg/collection/lib/src/utils.dart
+++ b/tests/lib/js/null_test.js
@@ -2,12 +2,6 @@
 // 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 dart.pkg.collection.utils;
-
-/// A pair of values.
-class Pair<E, F> {
-  E first;
-  F last;
-
-  Pair(this.first, this.last);
-}
+// This code is not inlined in the test to support testing in CSP mode.
+function isUndefined(o) { return o === undefined; }
+function isNull(o) { return o === null; }