Initializing formals can't be optional parameters

runtime/bin/socket.dart

 // Copyright (c) 2011, 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.
 
 interface ServerSocket factory _ServerSocket {
   /*
    * Constructs a new server socket, binds it to a given address and port,
    * and listens on it.
    */
   ServerSocket(String bindAddress, int port, int backlog);
@@ skipping 105 matching lines @@
    * and calling it several times is supported. If [halfClose] is true
    * the socket will only be closed for writing and it might still be
    * possible to read data. Calling [close] will not trigger a call to
    * the [closeHandler].
    */
   void close([bool halfClose]);
 }
 
 
 class SocketIOException implements Exception {
-  const SocketIOException([String this.message = ""]);
+  const SocketIOException([String message = ""])
+      : this.message = message;
   String toString() => "SocketIOException: $message";
 
   /*
    * Contains the exception message.
    */
   final String message;
 }