Migrating a block of dart 1 tests to dart 2

tests/language_2/closure_break_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.
 // Dart test for closures.
 
 import "package:expect/expect.dart";
 
 class ClosureBreak {
   ClosureBreak(this.field);
   int field;
@@ skipping 36 matching lines @@
       break L1;
     }
     foo();
     Expect.equals(4, o1.field);
   }
 }
 
 main() {
   ClosureBreakTest.testMain();
 }