Fix the loops break label test with Kernel.

tests/compiler/dart2js/kernel/loops_test.dart

 // Copyright (c) 2016, 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:test/test.dart';
 
 import 'helper.dart' show check;
 
 main() {
   test('for loop', () {
@@ skipping 65 matching lines @@
 main() {
   var sum = 0;
   for (a in [1, 2, 3]) {
     sum += a;
   }
   return sum;
 }''';
     return check(code, disableTypeInference: false);
   });
 
-  // TODO(efortuna): Fix and uncomment.
-  // See bug https://github.com/dart-lang/sdk/issues/28670
-  /*test('for loop with break to label', () {
+  test('for loop with break to label', () {
     String code = '''
 var a = 0;
 main() {
   var sum = 0;
   outer: for (a in [1, 2, 3]) {
     for (int i = 0; i < 10; i++) {
       sum += a;
       if (a + i < 5)
         break outer;
     }
   }
   return sum;
 }''';
     return check(code, disableTypeInference: false);
-  });*/
+  });
 }