Disable kernel unit tests.

pkg/kernel/test/type_subtype_test_disabled.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 'package:kernel/ast.dart';
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/type_environment.dart';
 import 'type_parser.dart';
 
@@ skipping 142 matching lines @@
         fail('isSubtypeOf(${testCase.subtype}, ${testCase.supertype}) returned '
             '${!testCase.isSubtype} but should return ${testCase.isSubtype}');
       }
       if (subtype != supertype && tester.isSubtypeOf(supertype, subtype)) {
         fail('isSubtypeOf(${testCase.supertype}, ${testCase.subtype}) returned '
             'true but should return false');
       }
     });
   }
 }