Revert "Switch libraries to using new tags."

sdk/lib/io/socket.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.
 
-part of dart.io;
-
 abstract class ServerSocket {
   /**
    * Constructs a new server socket, binds it to a given address and port,
    * and listens on it.
    */
   external factory ServerSocket(String bindAddress, int port, int backlog);
 
   /**
    * The connection handler gets called when there is a new incoming
    * connection on the socket.
@@ skipping 135 matching lines @@
         sb.add(" ($osError)");
       }
     } else if (osError != null) {
       sb.add(": $osError");
     }
     return sb.toString();
   }
   final String message;
   final OSError osError;
 }