Fix assertion in http-client.

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;
 
 const int _OUTGOING_BUFFER_SIZE = 8 * 1024;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
@@ skipping 1675 matching lines @@
 
   Future<HttpClientRequest> patch(String host, int port, String path)
       => open("patch", host, port, path);
 
   Future<HttpClientRequest> patchUrl(Uri url) => _openUrl("patch", url);
 
   void close({bool force: false}) {
     _closing = true;
     _connectionTargets.values.toList().forEach((c) => c.close(force));
     assert(!_connectionTargets.values.any((s) => s.hasIdle));
-    assert(!force || _connectionTargets.isEmpty);
+    assert(!force ||
+        !_connectionTargets.values.any((s) => s._active.isNotEmpty));
   }
 
   set authenticate(Future<bool> f(Uri url, String scheme, String realm)) {
     _authenticate = f;
   }
 
   void addCredentials(Uri url, String realm, HttpClientCredentials cr) =>
       _credentials.add(new _SiteCredentials(url, realm, cr));
 
   set authenticateProxy(
@@ skipping 1021 matching lines @@
   const _RedirectInfo(this.statusCode, this.method, this.location);
 }
 
 String _getHttpVersion() {
   var version = Platform.version;
   // Only include major and minor version numbers.
   int index = version.indexOf('.', version.indexOf('.') + 1);
   version = version.substring(0, index);
   return 'Dart/$version (dart:io)';
 }