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

tests/compiler/dart2js_native/native_equals_frog_test.dart

Index: tests/compiler/dart2js_native/native_equals_frog_test.dart
diff --git a/tests/compiler/dart2js_native/native_equals_frog_test.dart b/tests/compiler/dart2js_native/native_equals_frog_test.dart
index 95c98ee14c8ab0b39cc49f5f2d0b85c2387ef4a5..0b460b91bb067cad48be65c4840a25c721e542c7 100644
--- a/tests/compiler/dart2js_native/native_equals_frog_test.dart
+++ b/tests/compiler/dart2js_native/native_equals_frog_test.dart
@@ -22,14 +22,17 @@ class B {
 makeA() native;
 makeB() native;
 
-void setup() native """
-function A() {}
-function B() {}
-makeA = function(){return new A;};
-makeB = function(){return new B;};
-
-self.nativeConstructor(B);
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  function A() {}
+  function B() {}
+  makeA = function(){return new A()};
+  makeB = function(){return new B()};
+
+  self.nativeConstructor(B);
+})()""");
+}
 
 main() {
   nativeTesting();