Handle instantiation of native classes in closed_world2_test

pkg/compiler/lib/src/kernel/native_class_resolver.dart

-// Copyright (c) 2017, 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.
-
-part of dart2js.kernel.element_map;
-
-/// Interface for computing all native classes in a set of libraries.
-class KernelNativeClassResolver implements NativeClassResolver {
-  final KernelToElementMap elementMap;
-
-  KernelNativeClassResolver(this.elementMap);
-
-  Iterable<ClassEntity> computeNativeClasses(
-      Iterable<LibraryEntity> libraries) {
-    // TODO(johnniwinther): Implement this.
-    return const <ClassEntity>[];
-  }
-}