Add a sleep function to dart:io

runtime/platform/platform_headers.gypi

Index: runtime/platform/platform_headers.gypi
diff --git a/runtime/platform/platform_headers.gypi b/runtime/platform/platform_headers.gypi
index 514ad081986026923f4c841ad3c5a9b1d60a5363..3f02692c3748a98c6073ba09f5d301b04f781075 100644
--- a/runtime/platform/platform_headers.gypi
+++ b/runtime/platform/platform_headers.gypi
@@ -1,4 +1,4 @@
-# Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+# 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.
 
@@ -13,6 +13,7 @@
     'json.h',
     'floating_point.h',
     'floating_point_win.h',
+    'platform_os.h',
     'thread.h',
     'thread_linux.h',
     'thread_macos.h',