Clear http session object on destroy.

sdk/lib/io/http_impl.dart

 // Copyright (c) 2013, 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;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
   final Completer _dataCompleter = new Completer();
   Stream<List<int>> _stream;
@@ skipping 110 matching lines @@
     }
     return _queryParameters;
   }
 
   Uri get uri => _incoming.uri;
 
   String get method => _incoming.method;
 
   HttpSession get session {
     if (_session != null) {
+      if (_session._destroyed) {
+        // It's destroyed, clear it.
+        _session = null;
+        // Create new session object by calling recursive.
+        return session;
+      }
       // It's already mapped, use it.
       return _session;
     }
     // Create session, store it in connection, and return.
     return _session = _httpServer._sessionManager.createSession();
   }
 
   HttpConnectionInfo get connectionInfo => _httpConnection.connectionInfo;
 
   X509Certificate get certificate {
@@ skipping 1917 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }