dart2js_native tests: Migrate 'native STRING' to JS-calls - part 2/2

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}};
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  function A() {}
+  A.prototype.$isThing = true;
+  make1 = function(){return new A;};
+  make2 = function(){return {$isThing: true}};
+})()""");
+}
 
 inscrutable(x) {
   if (new DateTime.now().millisecondsSinceEpoch == 0) {
     return x;
   } else {
     return 42;
   }
 }
 
 main() {
   setup();
 
   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);
 }