Add File.renameSync() to virtual file system.

pkg/analyzer/lib/file_system/file_system.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.file_system.file_system;
 
 import 'dart:async';
 
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/util/absolute_path.dart';
@@ skipping 26 matching lines @@
    */
   List<int> readAsBytesSync();
 
   /**
    * Synchronously read the entire file contents as a [String].
    * Throws [FileSystemException] if the file does not exist.
    */
   String readAsStringSync();
 
   /**
+   * Synchronously rename this file.
+   * Return a [File] instance for the renamed file.
+   *
+   * If [newPath] identifies an existing file, that file is replaced.
+   * If [newPath] identifies an existing resource the operation might fail and
+   * an exception is thrown.
+   */
+  File renameSync(String newPath);
+
+  /**
    * Synchronously write a list of bytes to the file.
    *
    * Throws a [FileSystemException] if the operation fails.
    */
   void writeAsBytesSync(List<int> bytes);
 }
 
 /**
  * Base class for all file system exceptions.
  */
@@ skipping 158 matching lines @@
 
   @override
   Uri restoreAbsolute(Source source) =>
       _provider.pathContext.toUri(source.fullName);
 
   /**
    * Return `true` if the given [uri] is a `file` URI.
    */
   static bool _isFileUri(Uri uri) => uri.scheme == _FILE_SCHEME;
 }