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

tests/compiler/dart2js_native/native_call_arity3_frog_test.dart

Index: tests/compiler/dart2js_native/native_call_arity3_frog_test.dart
diff --git a/tests/compiler/dart2js_native/native_call_arity3_frog_test.dart b/tests/compiler/dart2js_native/native_call_arity3_frog_test.dart
index e0e05709e1e78ed2d683a81474fbb2b6a8c62066..cd7996bee277aae032b89c892f9b4f041bf9d882 100644
--- a/tests/compiler/dart2js_native/native_call_arity3_frog_test.dart
+++ b/tests/compiler/dart2js_native/native_call_arity3_frog_test.dart
@@ -24,19 +24,22 @@ class B {
 A makeA() native;
 B makeB() native;
 
-void setup() native """
-function A() {}
-A.prototype.foo = function () { return arguments.length; };
+void setup() {
+  JS('', r"""
+(function(){
+  function A() {}
+  A.prototype.foo = function () { return arguments.length; };
 
-function B() {}
-B.prototype.foo = function () { return arguments.length; };
+  function B() {}
+  B.prototype.foo = function () { return arguments.length; };
 
-makeA = function(){return new A;};
-makeB = function(){return new B;};
+  makeA = function(){return new A();};
+  makeB = function(){return new B();};
 
-self.nativeConstructor(A);
-self.nativeConstructor(B);
-""";
+  self.nativeConstructor(A);
+  self.nativeConstructor(B);
+})()""");
+}
 
 testDynamicContext() {
   var a = confuse(makeA());