Make dart2js_native/fake_thing_test fail again.

tests/compiler/dart2js_native/fake_thing_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.
 
 import "package:expect/expect.dart";
 
 // Test that native objects cannot accidentally or maliciously be mistaken for
 // Dart objects.
 
+// This test currently fails because we do not recognize the need for
+// interceptors without native *classes*.
+
 class Thing {
 }
 
 make1() native;
 make2() native;
 
 void setup() native r"""
 function A() {}
 A.prototype.$isThing = true;
 make1 = function(){return new A;};
 make2 = function(){return {$isThing: true}};
 """;
 
-var inscrutable;
+inscrutable(x) {
+  if (new DateTime.now().millisecondsSinceEpoch == 0) {
+    return x;
+  } else {
+    return 42;
+  }
+}
+
 main() {
   setup();
-  inscrutable = (x) => x;
 
   var a = new Thing();
   var b = make1();
   var c = make2();
   Expect.isTrue(inscrutable(a) is Thing);
   Expect.isFalse(inscrutable(b) is Thing);
   Expect.isFalse(inscrutable(c) is Thing);
 }