Fix private member name mangling.

frog/member_set.dart

 // Copyright (c) 2012, 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.
 
 class MemberSet {
   final String name;
   final List<Member> members;
-  final String jsname;
   final bool isVar;
+  String jsname;
+  bool jsnameUnique = false;
 
   bool _treatAsField;
   Type _returnTypeForGet;
   bool _preparedForSet = false;
   List<InvokeKey> _invokes;
 
   MemberSet(Member member, [bool isVar=false]):
     name = member.name, members = [member], jsname = member.jsname,
     isVar = isVar;
 
@@ skipping 270 matching lines @@
           returnType = world.varType;
         }
       }
     }
     if (returnType == null) {
       // TODO(jimhug): Warning here for no match anywhere in the world?
       returnType = world.varType;
     }
   }
 }