Fix standalone tests to pass dartc.

tests/standalone/io/http_10_test.dart

 // (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.
 
 // VMOptions=
 // VMOptions=--short_socket_read
 // VMOptions=--short_socket_write
 // VMOptions=--short_socket_read --short_socket_write
 
 import "package:expect/expect.dart";
+import "dart:async";
 import "dart:isolate";
 import "dart:io";
 
 // Client makes a HTTP 1.0 request without connection keep alive. The
 // server sets a content length but still needs to close the
 // connection as there is no keep alive.
 void testHttp10NoKeepAlive() {
   HttpServer.bind().then((server) {
     server.listen(
         (HttpRequest request) {
@@ skipping 203 matching lines @@
   });
 }
 
 
 void main() {
   testHttp10NoKeepAlive();
   testHttp10ServerClose();
   testHttp10KeepAlive();
   testHttp10KeepAliveServerCloses();
 }