Don't close existing connection on HttpServer close (and stream cancel).

tests/standalone/io/http_detach_socket_test.dart

Index: tests/standalone/io/http_detach_socket_test.dart
diff --git a/tests/standalone/io/http_detach_socket_test.dart b/tests/standalone/io/http_detach_socket_test.dart
index 6b38de25a0d9f787085a95d6972c6be2a4903cb1..cd03dfd7b0b248bdd1ea59a61362498fc2fb829e 100644
--- a/tests/standalone/io/http_detach_socket_test.dart
+++ b/tests/standalone/io/http_detach_socket_test.dart
@@ -60,10 +60,11 @@ void testBadServerDetachSocket() {
 
     Socket.connect("127.0.0.1", server.port).then((socket) {
       socket.write("GET / HTTP/1.1\r\n"
+                   "Connection: Close\r\n"
                    "content-length: 0\r\n\r\n");
       socket.listen((_) {}, onDone: () {
-          socket.close();
-        });
+        socket.close();
+      });
     });
   });
 }