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

tests/standalone/io/http_session_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:io");
 
 const SESSION_ID = "DARTSESSID";
 
 String getSessionId(List<Cookie> cookies) {
   var id = cookies.reduce(null, (last, cookie) {
@@ skipping 12 matching lines @@
   var c = new Completer();
   var client = new HttpClient();
   var conn = client.get("127.0.0.1", port, "/");
   conn.onRequest = (request) {
     if (session != null) {
       request.cookies.add(new Cookie(SESSION_ID, session));
     }
     request.outputStream.close();
   };
   conn.onResponse = (response) {
-    client.shutdown();
-    c.complete(getSessionId(response.cookies));
+    response.inputStream.onData = response.inputStream.read;
+    response.inputStream.onClosed = () {
+      client.shutdown();
+      c.complete(getSessionId(response.cookies));
+    };
   };
   return c.future;
 }
 
 void testSessions(int sessionCount) {
   HttpServer server = new HttpServer();
   server.listen("127.0.0.1", 0);
   var sessions = new Set();
   server.defaultRequestHandler = (request, response) {
     sessions.add(request.session().id);
@@ skipping 50 matching lines @@
         server.close();
       });
     });
   });
 }
 
 void main() {
   testSessions(5);
   testTimeout(5);
 }