Fix bad assert in constant evaluation.

tests/language/indirect_const_null_test.dart

 // Copyright (c) 2015, 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 error_at_spawnuri_iso;
+import "package:expect/expect.dart";
 
 main() {
-  throw new ArgumentError("fast error");
+  const NULL = 1 == 1 ? null : false;
+  Expect.isNull(NULL);
 }