Make StreamSubscription be the active part of a stream.

tests/standalone/io/http_redirect_test.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.
 //
 
 import "package:expect/expect.dart";
 import "dart:async";
 import "dart:io";
 import "dart:uri";
 
@@ skipping 179 matching lines @@
          Expect.fail("Redirect of POST should not happen");
        }
     );
 
     // Setup redirect for 303 where POST should turn into GET.
     addRequestHandler(
         "/303src",
         (HttpRequest request, HttpResponse response) {
           request.listen((_) {}, onDone: () {
             Expect.equals("POST", request.method);
-            request.listen(
-                (_) {},
-                onDone: () {
-                  response.headers.set(
-                      HttpHeaders.LOCATION,
-                      "http://127.0.0.1:${server.port}/303target");
-                  response.statusCode = HttpStatus.SEE_OTHER;
-                  response.close();
-                });
+            response.headers.set(
+                HttpHeaders.LOCATION,
+                "http://127.0.0.1:${server.port}/303target");
+            response.statusCode = HttpStatus.SEE_OTHER;
+            response.close();
           });
         });
     addRequestHandler(
        "/303target",
        (HttpRequest request, HttpResponse response) {
          Expect.equals("GET", request.method);
          response.close();
        });
 
     // Setup redirect where we close the connection.
@@ skipping 247 matching lines @@
   testManualRedirectWithHeaders();
   testAutoRedirect();
   testAutoRedirectWithHeaders();
   testAutoRedirect301POST();
   testAutoRedirect303POST();
   testAutoRedirectLimit();
   testRedirectLoop();
   testRedirectClosingConnection();
   testRedirectRelativeUrl();
 }