Add a sleep function to dart:io

runtime/platform/platform_os_macos.cc

+// 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.
+
+#include "platform/globals.h"
+#if defined(TARGET_OS_MACOS)
+
+#include "platform/platform_os.h"
+
+#include <unistd.h>  // NOLINT
+
+namespace platform {
+
+void OS::Sleep(int64_t millis) {
+  // TODO(5411554):  For now just use usleep we may have to revisit this.
+  usleep(millis * 1000);
+}
+
+}  // namespace platform
+
+#endif  // defined(TARGET_OS_MACOS)