Add support for directory renaming to dart:io.

runtime/bin/directory_posix.cc

 // Copyright (c) 2012, 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 "bin/directory.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <sys/param.h>
 #include <sys/stat.h>
@@ skipping 405 matching lines @@
 }
 
 
 bool Directory::Delete(const char* dir_name, bool recursive) {
   if (!recursive) {
     return (TEMP_FAILURE_RETRY(remove(dir_name)) == 0);
   } else {
     return DeleteRecursively(dir_name);
   }
 }
+
+
+bool Directory::Rename(const char* path, const char* new_path) {
+  ExistsResult exists = Exists(path);
+  if (exists != EXISTS) return false;
+  return (TEMP_FAILURE_RETRY(rename(path, new_path)) == 0);
+}