Refactor the close and error handling of HTTP connections

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,
                            bool this._closeAsError,
-                           SocketImpl this._socket);
+                           SocketMock this._socket);
 
   void set onNoPendingWrites(void callback()) {
     _onNoPendingWrites = callback;
   }
 
   bool write(List data, [bool copyBuffer = true]) {
     _onData(data);
     return true;
   }
 
@@ skipping 19 matching lines @@
       // Tell HttpServer that the socket have closed.
       _socket._closeInternal(_closeAsError);
     }
   }
 
   Function _onNoPendingWrites;
   List<int> _data;
   int _written = 0;
   int _cutoff;
   bool _closeAsError;
-  SocketImpl _socket;
+  SocketMock _socket;
 }
 
 class SocketMock implements Socket {
   SocketMock(List<int> this._data,
              List<int> expected,
              int cutoff,
              bool closeAsError) :
       _hashCode = (Math.random() * (1 << 32)).toInt(),
       _read = [] {
     _outputStream =
@@ skipping 141 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();
 }