Fix type warning.

tests/standalone/src/SocketCloseTest.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.
 //
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 //
 // Test socket close events.
@@ skipping 176 matching lines @@
   ReceivePort _receivePort;
   SendPort _sendPort;
   Socket _socket;
   List<int> _buffer;
   int _readBytes;
   int _dataEvents;
   int _closeEvents;
   int _errorEvents;
   int _iterations;
   int _mode;
-  int _donePort;
+  SendPort _donePort;
 }
 
 
 class ConnectionData {
   ConnectionData(Socket this.connection) : readBytes = 0;
   Socket connection;
   int readBytes;
 }
 
 
@@ skipping 171 matching lines @@
   var tests = 7;
   var port = new ReceivePort();
   var completed = 0;
   port.receive((message, ignore) {
     if (++completed == tests) port.close();
   });
   for (var i = 0; i < tests; i++) {
     new SocketClose.start(i, port.toSendPort());
   }
 }