Re-enable kernel unit tests on platforms where they are supported.

pkg/kernel/test/baseline_strong_mode_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:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
 import 'package:kernel/kernel.dart';
 import 'package:kernel/transformations/mixin_full_resolution.dart';
 import 'package:kernel/type_checker.dart';
 import 'package:path/path.dart' as pathlib;
 
@@ skipping 43 matching lines @@
     } else {
       locationString = '(no location)';
     }
     errors.add('$message $locationString');
   }
 }
 
 void main() {
   runBaselineTests('strong-mode', new StrongModeTest());
 }