- Add needed enum flags for dart2js.

tests/language/enum_const_test.dart

 // Copyright (c) 2014, 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
+
 import "dart:isolate";
 import "package:expect/expect.dart";
 
 enum Foo {
   BAR, BAZ
 }
 
 verify(val) {
   Expect.identical(Foo.BAR, val);
 }
 
 main() {
   verify(Foo.BAR);
   var rp;
   rp = new RawReceivePort((val) {
     verify(val);
     rp.close();
   });
   rp.sendPort.send(Foo.BAR);
 }