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

tests/compiler/dart2js_native/native_wrapping_function3_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";
 
 typedef void Callback0();
 typedef void Callback1(arg1);
 typedef void Callback2(arg1, arg2);
 
 @Native("A")
 class A {
   foo1(Callback1 closure, [arg1 = 0]) native;
   foo2(Callback2 closure, [arg1 = 0, arg2 = 1]) native;
 }
 
 A makeA() native;
 
-void setup() native """
-function A() {}
-A.prototype.foo1 = function(closure, arg1) { return closure(arg1); };
-A.prototype.foo2 = function(closure, arg1, arg2) {
-  return closure(arg1, arg2);
-};
-makeA = function(){return new A;};
-self.nativeConstructor(A);
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  function A() {}
+  A.prototype.foo1 = function(closure, arg1) { return closure(arg1); };
+  A.prototype.foo2 = function(closure, arg1, arg2) {
+    return closure(arg1, arg2);
+  };
+  makeA = function(){return new A()};
+  self.nativeConstructor(A);
+})()""");
+}
 
 main() {
   nativeTesting();
   setup();
   var a = makeA();
   // Statically known receiver type calls.
   Expect.equals(43, a.foo1((arg1) => arg1, 43));
   Expect.equals(0, a.foo1((arg1) => arg1));
 
   Expect.equals(44, a.foo2((arg1, arg2) => arg1 + arg2, 21, 23));
   Expect.equals(22, a.foo2((arg1, arg2) => arg1 + arg2, 21));
 
   // Dynamic calls.
   Expect.equals(43, confuse(a).foo1((arg1) => arg1, 43));
   Expect.equals(0, confuse(a).foo1((arg1) => arg1));
 
   Expect.equals(44, confuse(a).foo2((arg1, arg2) => arg1 + arg2, 21, 23));
   Expect.equals(22, confuse(a).foo2((arg1, arg2) => arg1 + arg2, 21));
 }