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

tests/compiler/dart2js_native/oddly_named_fields_test.dart

Index: tests/compiler/dart2js_native/oddly_named_fields_test.dart
diff --git a/tests/compiler/dart2js_native/oddly_named_fields_test.dart b/tests/compiler/dart2js_native/oddly_named_fields_test.dart
index 717e296713acf2437754ed5b16a676e68d331e39..54d9bd48d7a4387cc9e19d90836a59bc52df9fe5 100644
--- a/tests/compiler/dart2js_native/oddly_named_fields_test.dart
+++ b/tests/compiler/dart2js_native/oddly_named_fields_test.dart
@@ -1381,11 +1381,14 @@ testObjectWeaklyTyped(object) {
 
 NativeClassWithOddNames makeNativeClassWithOddNames() native;
 
-setup() native """
-function NativeClassWithOddNames() {}
-makeNativeClassWithOddNames = function() { return new NativeClassWithOddNames; }
-self.nativeConstructor(NativeClassWithOddNames);
-""";
+setup() {
+  JS('', r"""
+(function(){
+  function NativeClassWithOddNames() {}
+  makeNativeClassWithOddNames = function() {return new NativeClassWithOddNames()};
+  self.nativeConstructor(NativeClassWithOddNames);
+})()""");
+}
 
 main() {
   nativeTesting();