Fix a number of editor errors and warnings in io tests

tests/standalone/src/io/HttpServerSocketTest.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.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class ExpectedDataOutputStream implements OutputStream {
   ExpectedDataOutputStream(List<int> this._data,
                            int this._cutoff,
@@ skipping 129 matching lines @@
   }
 
   void close() {
     Expect.fail("Don't close the connection, we attach to this socket");
   }
 
   void set onConnection(void callback(Socket connection)) {
     _onConnection = callback;
   }
 
-  void set onError(void callback()) {
+  void set onError(void callback(Exception)) {
     _onError = callback;
   }
 
   int get port() => _port;
 
   int _port;
   Function _onConnection;
   Function _onError;
   Set<Socket> _sockets;
 }
@@ skipping 44 matching lines @@
       "GET / HTTP/1.1\r\nKeep-Alive: False\r\n\r\n",
       "HTTP/1.1 200 OK\r\ntransfer-encoding: chunked\r\nconnection: close" +
       "\r\n\r\n0\r\n\r\n");
 
   server.close();
 }
 
 void main() {
   testSocketClose();
 }