dart2js_native tests: Migrate 'native STRING' to JS-calls

tests/compiler/dart2js_native/super_property_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 "native_testing.dart";
 
 // Tests super setter where the HInvokeSuper is using interceptor aka
 // explicit-receiver calling convention.
 
 @Native("A")
@@ skipping 22 matching lines @@
   set foo(value) {
     super.foo = value;
   }
 
   get foo => super.foo;
 }
 
 makeA() native;
 makeB() native;
 
-void setup() native """
-// This code is all inside 'setup' and so not accessible from the global scope.
-function A(){}
-function B(){}
-makeA = function(){return new A};
-makeB = function(){return new B};
-self.nativeConstructor(A);
-self.nativeConstructor(B);
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  // This code is inside 'setup' and so not accessible from the global scope.
+  function A(){}
+  function B(){}
+  makeA = function(){return new A()};
+  makeB = function(){return new B()};
+  self.nativeConstructor(A);
+  self.nativeConstructor(B);
+})()""");
+}
 
 testThing(a) {
   a.foo = 123;
   Expect.equals(123, a.foo);
   Expect.equals(123, a.get_foo());
 
   a.bar = 234;
   Expect.equals(234, a.foo);
   Expect.equals(234, a.get_foo());
 }
 
 main() {
   nativeTesting();
   setup();
   var things = [makeA(), makeB(), new C(), new D()];
   var test = testThing;
   test(things[0]);
   test(things[1]);
   test(things[2]);
   test(things[3]);
 }