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

tests/compiler/dart2js_native/native_field_rename_1_frog_test.dart

Index: tests/compiler/dart2js_native/native_field_rename_1_frog_test.dart
diff --git a/tests/compiler/dart2js_native/native_field_rename_1_frog_test.dart b/tests/compiler/dart2js_native/native_field_rename_1_frog_test.dart
index c8bed68c8a28f423dca7dafcde796ebf4d72e03f..5fd66023d9ad92faee548b38e1b49ce4a17447e1 100644
--- a/tests/compiler/dart2js_native/native_field_rename_1_frog_test.dart
+++ b/tests/compiler/dart2js_native/native_field_rename_1_frog_test.dart
@@ -33,20 +33,23 @@ class X {
 A makeA() native;
 X makeX() native;
 
-void setup() native """
-// This code is all inside 'setup' and so not accessible from the global scope.
-function A(){ this.key = 111; }
-A.prototype.getKey = function(){return this.key;};
-
-function X(){}
-X.prototype.key = function(){return 666;};
-
-makeA = function(){return new A};
-makeX = function(){return new X};
-
-self.nativeConstructor(A);
-self.nativeConstructor(X);
-""";
+void setup() {
+  JS('', r"""
+(function(){
+  // This code is inside 'setup' and so not accessible from the global scope.
+  function A(){ this.key = 111; }
+  A.prototype.getKey = function(){return this.key;};
+
+  function X(){}
+  X.prototype.key = function(){return 666;};
+
+  makeA = function(){return new A()};
+  makeX = function(){return new X()};
+
+  self.nativeConstructor(A);
+  self.nativeConstructor(X);
+})()""");
+}
 
 testDynamic() {
   var a = confuse(makeA());