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

tests/standalone/io/http_proxy_test.dart

Index: tests/standalone/io/http_proxy_test.dart
diff --git a/tests/standalone/io/http_proxy_test.dart b/tests/standalone/io/http_proxy_test.dart
index aa179632ed61c9845749101f5bdfda57b0d4943e..3f2d0cf9a6a73c9beba24857727f7a4da82bf99e 100644
--- a/tests/standalone/io/http_proxy_test.dart
+++ b/tests/standalone/io/http_proxy_test.dart
@@ -104,8 +104,7 @@ class ProxyServer {
             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);