Add error handling to the HTTP library

runtime/bin/socket_stream_impl.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.
 
 class _SocketInputStream implements SocketInputStream {
   _SocketInputStream(Socket socket) : _socket = socket {
     if (_socket._id == -1) _closed = true;
     _socket.onClosed = _onClosed;
   }
 
@@ skipping 156 matching lines @@
       }
     }
 
     // All buffered data was written.
     if (_closing) {
       _socket._closeWrite();
       _closed = true;
     } else {
       if (_onNoPendingWrites != null) _onNoPendingWrites();
     }
-    if (_onNoPendingWrites == null) _socket._onWrite = null;
+    if (_onNoPendingWrites == null) {
+      _socket._onWrite = null;
+    } else {
+      _socket._onWrite = _onWrite;
+    }
   }
 
   void set onError(void callback(Exception e)) {
     _errorCallback = callback;
   }
 
   void _onError(Exception e) {
     close();
     if (_errorCallback != null) _errorCallback(e);
   }
 
   Socket _socket;
   _BufferList _pendingWrites;
   var _onNoPendingWrites;
   Function _errorCallback;
   bool _closing = false;
   bool _closed = false;
 }