Add HttpServer.idleTimeout for closing idle keep-alive connections.

tests/standalone/io/http_server_idle_timeout_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.
+//
+// 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:io";
+import "dart:isolate";
+
+
+void testTimeoutAfterRequest() {
+  HttpServer.bind("127.0.0.1", 0).then((server) {
+    server.idleTimeout = const Duration(milliseconds: 100);
+
+    server.listen((request) => request.response.close());
+
+    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.listen(
+          null,
+          onDone: () {
+            socket.close();
+            server.close();
+          });
+    });
+  });
+}
+
+void testTimeoutBeforeRequest() {
+  HttpServer.bind("127.0.0.1", 0).then((server) {
+    server.idleTimeout = const Duration(milliseconds: 100);
+
+    server.listen((request) => request.response.close());
+
+    Socket.connect("127.0.0.1", server.port).then((socket) {
+      socket.listen(
+          null,
+          onDone: () {
+            socket.close();
+            server.close();
+          });
+    });
+  });
+}
+
+void main() {
+  testTimeoutAfterRequest();
+  testTimeoutBeforeRequest();
+}