Make Completers asynchronous.

tests/standalone/io/http_server_early_client_close2_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:isolate";
+
+main() {
+  HttpServer.bind("127.0.0.1", 0).then((server) {
+    server.listen(
+      (request) {
+        String name = new Options().script;
+        new File(name).openRead().pipe(request.response)
+            .catchError((e) { /* ignore */ });
+      });
+
+    var count = 0;
+    makeRequest() {
+      Socket.connect("127.0.0.1", server.port).then((socket) {
+        var data = "GET / HTTP/1.1\r\nContent-Length: 0\r\n\r\n";
+        socket.write(data);
+        socket.close();
+        socket.done.then((_) {
+          socket.destroy();
+          if (++count < 10) {
+            makeRequest();
+          } else {
+            server.close();
+          }
+        });
+      });
+    }
+    makeRequest();
+  });
+}