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

pkg/kernel/test/type_substitution_identity_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/kernel.dart';
 import 'package:kernel/type_algebra.dart';
 import 'type_parser.dart';
-import 'type_unification_test_disabled.dart' show testCases;
+import 'type_unification_test.dart' show testCases;
 import 'package:test/test.dart';
 
 checkType(DartType type) {
   var map = {new TypeParameter(): const DynamicType()};
   var other = substitute(type, map);
   if (!identical(type, other)) {
     fail('Identity substitution test failed for $type');
   }
   other = Substitution.fromUpperAndLowerBounds(map, map).substituteType(type);
   if (!identical(type, other)) {
     fail('Identity bounded substitution test failed for $type');
   }
 }
 
 main() {
   for (var testCase in testCases) {
     test('$testCase', () {
       var env = new LazyTypeEnvironment();
       checkType(env.parse(testCase.type1));
       checkType(env.parse(testCase.type2));
     });
   }
 }