dart:io | Add rename() and renameSync() to FileSystem Entity

sdk/lib/io/file_system_entity.dart

 // 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.
 
 part of dart.io;
 
 class FileSystemEntityType {
   static const FILE = const FileSystemEntityType._internal(0);
   static const DIRECTORY = const FileSystemEntityType._internal(1);
   static const LINK = const FileSystemEntityType._internal(2);
@@ skipping 253 matching lines @@
    * [Directory], and [Link].  Calling [existsSync] on an instance of
    * one of these subclasses checks whether the object exists in the
    * file system object exists and is of the correct type (file,
    * directory, or link).  To check whether a path points to an object
    * on the file system, regardless of the object's type, use the
    * [typeSync] static method.
    */
   bool existsSync();
 
   /**
+   * Renames this file system entity. Returns a `Future<FileSystemEntity>`
+   * that completes with a [FileSystemEntity] instance for the renamed
+   * file system entity.
+   *
+   * If [newPath] identifies an existing entity of the same type, that entity
+   * is replaced. If [newPath] identifies an existing entity of a different
+   * type, the operation fails and the future completes with an exception.
+   */
+  Future<FileSystemEntity> rename(String newPath);
+
+   /**
+   * Synchronously renames this file system entity. Returns a [FileSystemEntity]
+   * instance for the renamed entity.
+   *
+   * If [newPath] identifies an existing entity of the same type, that entity
+   * is replaced. If [newPath] identifies an existing entity of a different
+   * type, the operation fails and an exception is thrown.
+   */
+  FileSystemEntity renameSync(String newPath);
+
+  /**
    * Calls the operating system's stat() function on the [path] of this
    * [FileSystemEntity].  Identical to [:FileStat.stat(this.path):].
    *
    * Returns a [:Future<FileStat>:] object containing the data returned by
    * stat().
    *
    * If the call fails, completes the future with a [FileStat] object
    * with .type set to
    * FileSystemEntityType.NOT_FOUND and the other fields invalid.
    */
@@ skipping 86 matching lines @@
 
 
   static _throwIfError(Object result, String msg) {
     if (result is OSError) {
       throw new FileException(msg, result);
     } else if (result is ArgumentError) {
       throw result;
     }
   }
 }