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

tests/compiler/dart2js_native/native_missing_method2_frog_test.dart

 // Copyright (c) 2012, 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';
 
 @Native("A")
 class A {}
 
 A makeA() native;
 
-void setup() native """
-function A() {};
-A.prototype.foo = function() { return  42; }
-makeA = function() { return new A; }
-self.nativeConstructor(A);
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  function A() {};
+  A.prototype.foo = function() { return  42; };
+  makeA = function() { return new A() };
+  self.nativeConstructor(A);
+})()""");
+}
 
 class B {
   foo() {
     return 42;
   }
 }
 
 class C {
   // By having two 'foo' defined in the application, Frog will mangle
   // all calls to 'foo', which makes this test pass.
@@ skipping 17 matching lines @@
 }
 
 main() {
   nativeTesting();
   setup();
   confuse(new B()).foo();
   confuse(new C()).foo(1);
   typedContext();
   untypedContext();
 }