Enable a couple of tests that were disabled because they

tests/standalone/io/regress-6521.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.
-//
-// Regression test for http://code.google.com/p/dart/issues/detail?id=6393.
-
-import "dart:io";
-import "dart:uri";
-
-var client = new HttpClient();
-var clientRequest;
-
-void main() {
-  var server = new HttpServer();
-  server.listen("127.0.0.1", 0);
-  server.defaultRequestHandler = (req, rsp) {
-    req.inputStream.onData = () {
-      req.inputStream.read();
-      rsp.outputStream.close();
-    };
-    req.inputStream.onClosed = () {
-      client.shutdown();
-      server.close();
-    };
-  };
-
-  var connection = client.openUrl(
-      "POST",
-      new Uri.fromString("http://localhost:${server.port}/"));
-  connection.onRequest = (request) {
-    // Keep a reference to the client request object.
-    clientRequest = request;
-    request.outputStream.write([0]);
-  };
-  connection.onResponse = (response) {
-    response.inputStream.onClosed = () {
-      // Wait with closing the client request until the response is done.
-      clientRequest.outputStream.close();
-    };
-  };
-}