Support enums in dart2dart.

tests/language/enum_duplicate_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 for duplicate enums.
+
+library enum_duplicate_test;
+
+import 'package:expect/expect.dart';
+
+import 'enum_duplicate_lib.dart' as lib; /// 01: ok
+
+enum Enum {
+  A,
+  B,
+}
+
+main() {
+  Expect.equals('Enum.A,Enum.B', Enum.values.join(','));
+  Expect.equals('Enum.A,Enum.B', lib.Enum.values.join(',')); /// 01: continued
+}
+
+
+