Remove HttpClientRequest.response, as it's identical to HttpClientRequest.done.

tests/standalone/io/http_proxy_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";
 
 class Server {
@@ skipping 86 matching lines @@
                 }
               });
             });
             // Special handling of Content-Length and Via.
             clientRequest.contentLength = request.contentLength;
             List<String> via = request.headers[HttpHeaders.VIA];
             String viaPrefix = via == null ? "" : "${via[0]}, ";
             clientRequest.headers.add(
                 HttpHeaders.VIA, "${viaPrefix}1.1 localhost:$port");
             // Copy all content.
-            request.pipe(clientRequest);
-            return clientRequest.response;
+            return request.pipe(clientRequest);
           })
           .then((HttpClientResponse clientResponse) {
             clientResponse.pipe(request.response);
           });
       });
     });
     return x.future;
   }
 
   void shutdown() {
@@ skipping 294 matching lines @@
   InitializeSSL();
   testInvalidProxy();
   testDirectProxy();
   testProxy();
   testProxyChain();
   testProxyFromEnviroment();
   // This test is not normally run. It can be used for locally testing
   // with a real proxy server (e.g. Apache).
   //testRealProxy();
 }