Generate an error for active connections when the HTTP client is shutdown

tests/standalone/io/http_connection_header_test.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:isolate");
 #import("dart:io");
 
 void setConnectionHeaders(HttpHeaders headers) {
   headers.add(HttpHeaders.CONNECTION, "my-connection-header1");
@@ skipping 46 matching lines @@
     conn.onError = (e) => Expect.fail("Unexpected error $e");
     conn.onRequest = (HttpClientRequest request) {
       setConnectionHeaders(request.headers);
       request.persistentConnection = clientPersistentConnection;
       request.outputStream.close();
     };
     conn.onResponse = (HttpClientResponse response) {
       Expect.isFalse(response.persistentConnection);
       checkExpectedConnectionHeaders(response.headers,
                                      response.persistentConnection);
-      count++;
-      if (count == totalConnections) {
-        client.shutdown();
-        server.close();
-      }
+      response.inputStream.onClosed = () {
+        count++;
+        if (count == totalConnections) {
+          client.shutdown();
+          server.close();
+        }
+      };
     };
   }
 }
 
 
 void main() {
   test(2, false);
   test(2, true);
 }