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

tests/compiler/dart2js_native/native_property_frog_test.dart

Index: tests/compiler/dart2js_native/native_property_frog_test.dart
diff --git a/tests/compiler/dart2js_native/native_property_frog_test.dart b/tests/compiler/dart2js_native/native_property_frog_test.dart
index ae68f6e75f7b98a6cfcc2dc85e13030546b509c1..f8d2c20d27868954b9b03de362fbeef705d740af 100644
--- a/tests/compiler/dart2js_native/native_property_frog_test.dart
+++ b/tests/compiler/dart2js_native/native_property_frog_test.dart
@@ -25,18 +25,21 @@ class A {
 
 A makeA() native;
 
-void setup() native """
-function A() {}
+void setup() {
+  JS('', r"""
+(function(){
+  function A() {}
 
-Object.defineProperty(A.prototype, "X", {
-  get: function () { return this._x; },
-  set: function (v) { this._x = v; }
-});
+  Object.defineProperty(A.prototype, "X", {
+    get: function () { return this._x; },
+    set: function (v) { this._x = v; }
+  });
 
-makeA = function(){return new A;};
+  makeA = function(){return new A()};
 
-self.nativeConstructor(A);
-""";
+  self.nativeConstructor(A);
+})()""");
+}
 
 
 main() {