Support enums in dart2dart.

tests/language/enum_private_test.dart

+// Copyright (c) 2015, 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.
+
+// SharedOptions=--enable-enum
+
+// Test privacy issue for enums.
+
+library enum_private_test;
+
+import 'package:expect/expect.dart';
+
+import 'enum_private_lib.dart';
+
+enum Enum1 {
+  _A,
+  _B,
+}
+
+main() {
+  Expect.equals('Enum1._A,Enum1._B', Enum1.values.join(','));
+  Expect.equals('Enum2._A,Enum2._B', Enum2.values.join(',')); /// 01: ok
+  Expect.throws(() => Enum2._A, (e) => e is NoSuchMethodError); /// 02: static type warning
+}
+
+
+