Change File.directory to not do any IO

tests/standalone/io/file_non_ascii_sync_test.dart

 // 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.
 
 import "package:expect/expect.dart";
 import 'dart:io';
 
 main() {
   Directory tempDir = new Directory('').createTempSync();
   Directory nonAsciiDir = new Directory('${tempDir.path}/æøå');
   nonAsciiDir.createSync();
   Expect.isTrue(nonAsciiDir.existsSync());
   File nonAsciiFile = new File('${nonAsciiDir.path}/æøå.txt');
   nonAsciiFile.writeAsStringSync('æøå');
   Expect.isTrue(nonAsciiFile.existsSync());
   // On MacOS you get the decomposed utf8 form of file and directory
   // names from the system. Therefore, we have to check for both here.
   var precomposed = 'æøå';
   var decomposed = new String.fromCharCodes([47, 230, 248, 97, 778]);
   // The contents of the file is precomposed utf8.
   Expect.equals(precomposed, nonAsciiFile.readAsStringSync());
   nonAsciiFile.createSync();
-  var path = nonAsciiFile.directorySync().path;
+  var path = nonAsciiFile.directory.path;
   Expect.isTrue(path.endsWith(precomposed) || path.endsWith(decomposed));
   Expect.equals(6, nonAsciiFile.lengthSync());
   nonAsciiFile.lastModifiedSync();
   path = nonAsciiFile.fullPathSync();
   Expect.isTrue(path.endsWith('${precomposed}.txt') ||
                 path.endsWith('${decomposed}.txt'));
   tempDir.deleteSync(recursive: true);
 }