Migrating a block of dart 1 tests to dart 2

tests/language_2/closure_shared_state_test.dart

 // Copyright (c) 2011, 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 "package:expect/expect.dart";
 
 // Tests for closures sharing mutable bindings.
 
 var f;
 var g;
@@ skipping 56 matching lines @@
   Expect.equals(200, f(300));
   Expect.equals(300, g(400));
   Expect.equals(400, g(500));
 }
 
 main() {
   test(setupPlain);
   test(setupLoop);
   test(setupNestedLoop);
 }