dart2js: run dartfmt on tests

tests/compiler/dart2js_native/native_to_string_frog_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:_js_helper";
 import "package:expect/expect.dart";
 
 @Native("A")
 class A {}
-makeA() native;
+
+makeA() native ;
 
 void setup() native """
 function A() {}
 makeA = function(){return new A;};
 """;
 
-
 main() {
   setup();
   Expect.isTrue(makeA().toString() is String);
 }