Add a sleep function to dart:io

runtime/platform/platform_os.h

Index: runtime/platform/platform_os.h
diff --git a/runtime/platform/platform_os.h b/runtime/platform/platform_os.h
new file mode 100644
index 0000000000000000000000000000000000000000..9bb2cb450796888c57fe5100917d75c408bd341b
--- /dev/null
+++ b/runtime/platform/platform_os.h
@@ -0,0 +1,19 @@
+// 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.
+
+#ifndef PLATFORM_PLATFORM_OS_H_
+#define PLATFORM_PLATFORM_OS_H_
+
+namespace platform {
+
+// Interface to the underlying OS platform.
+class OS {
+ public:
+  // Sleep the currently executing thread for millis ms.
+  static void Sleep(int64_t millis);
+};
+
+}  // namespace dart
+
+#endif  // PLATFORM_PLATFORM_OS_H_