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

tests/compiler/dart2js_native/native_field_rename_2_frog_test.dart

 // Copyright (c) 2011, 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.
 
 // A native method prevents other members from having that name, including
 // fields.  However, native fields keep their name.  The implication: a getter
 // for the field must be based on the field's name, not the field's jsname.
 
 import 'native_testing.dart';
 
@@ skipping 18 matching lines @@
   @JSName('key')
   int native_key_method() native;
   // This should cause B.key to be renamed, but not A.key.
   @JSName('key')
   int key() native;
 }
 
 A makeA() native;
 X makeX() native;
 
-void setup() native """
-// This code is all inside 'setup' and so not accessible from the global scope.
-function A(){ this.key = 111; }
-A.prototype.getKey = function(){return this.key;};
+void setup() {
+  JS('', r"""
+(function(){
+  // This code is inside 'setup' and so not accessible from the global scope.
+  function A(){ this.key = 111; }
+  A.prototype.getKey = function(){return this.key;};
 
-function X(){}
-X.prototype.key = function(){return 666;};
+  function X(){}
+  X.prototype.key = function(){return 666;};
 
-makeA = function(){return new A};
-makeX = function(){return new X};
+  makeA = function(){return new A()};
+  makeX = function(){return new X()};
 
-self.nativeConstructor(A);
-self.nativeConstructor(X);
-""";
+  self.nativeConstructor(A);
+  self.nativeConstructor(X);
+})()""");
+}
 
 testDynamic() {
   var a = confuse(makeA());
   var b = confuse(new B());
   var x = confuse(makeX());
 
   Expect.equals(111, a.key);
   Expect.equals(222, b.key);
   Expect.equals(111, a.getKey());
   Expect.equals(222, b.getKey());
@@ skipping 29 matching lines @@
 }
 
 main() {
   nativeTesting();
   setup();
 
   testTyped();
   testPartial();
   testDynamic();
 }