Reapply "Add a sleep function to dart:io"

sdk/lib/io/process.dart

Index: sdk/lib/io/process.dart
diff --git a/sdk/lib/io/process.dart b/sdk/lib/io/process.dart
index e3c62e977fe925f71d84a88d342c8902da4b1163..8ceb41d9e7d16a61d188b22901800cdfadccc91d 100644
--- a/sdk/lib/io/process.dart
+++ b/sdk/lib/io/process.dart
@@ -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.
 
@@ -9,6 +9,7 @@ part of dart.io;
 class _ProcessUtils {
   external static _exit(int status);
   external static _setExitCode(int status);
+  external static _sleep(int millis);
 }
 
 /**
@@ -39,6 +40,16 @@ set exitCode(int status) {
 }
 
 /**
+ * Sleep for the duration specified in [duration].
+ *
+ * Use this with care, as no asynchronous operations can be processed
+ * in a isolate while it is blocked in a [sleep] call.
+ */
+void sleep(Duration duration) {
+  _ProcessUtils._sleep(duration.inMilliseconds);
+}
+
+/**
  * [Process] is used to start new processes using the static
  * [start] and [run] methods.
  */