dart:io | Add Link.targetSync on all platforms.

tests/standalone/io/windows_file_system_links_test.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.
 
 import "dart:io";
 import "dart:isolate";
 
 testJunctionTypeDelete() {
   var temp = new Directory('').createTempSync();
   var x = '${temp.path}${Platform.pathSeparator}x';
   var y = '${temp.path}${Platform.pathSeparator}y';
 
   new Directory(x).createSync();
   new Link(y).create(x).then((_) {
     Expect.isTrue(new Directory(y).existsSync());
     Expect.isTrue(new Directory(x).existsSync());
     Expect.isTrue(FileSystemEntity.isLinkSync(y));
     Expect.isFalse(FileSystemEntity.isLinkSync(x));
     Expect.isTrue(FileSystemEntity.isDirectorySync(y));
     Expect.isTrue(FileSystemEntity.isDirectorySync(x));
     Expect.equals(FileSystemEntityType.DIRECTORY,
                   FileSystemEntity.typeSync(y));
     Expect.equals(FileSystemEntityType.DIRECTORY,
                   FileSystemEntity.typeSync(x));
     Expect.equals(FileSystemEntityType.LINK,
                   FileSystemEntity.typeSync(y, followLinks: false));
     Expect.equals(FileSystemEntityType.DIRECTORY,
                   FileSystemEntity.typeSync(x, followLinks: false));
+    Expect.equals(x, new Link(y).targetSync());
+
     // Test Junction pointing to a missing directory.
     new Directory(x).deleteSync();
     Expect.isTrue(new Directory(y).existsSync());
     Expect.isFalse(new Directory(x).existsSync());
     Expect.isTrue(FileSystemEntity.isLinkSync(y));
     Expect.isFalse(FileSystemEntity.isLinkSync(x));
     Expect.isFalse(FileSystemEntity.isDirectorySync(y));
     Expect.isFalse(FileSystemEntity.isDirectorySync(x));
     Expect.equals(FileSystemEntityType.NOT_FOUND,
                   FileSystemEntity.typeSync(y));
     Expect.equals(FileSystemEntityType.NOT_FOUND,
                   FileSystemEntity.typeSync(x));
     Expect.equals(FileSystemEntityType.LINK,
                   FileSystemEntity.typeSync(y, followLinks: false));
     Expect.equals(FileSystemEntityType.NOT_FOUND,
                   FileSystemEntity.typeSync(x, followLinks: false));
+    Expect.equals(x, new Link(y).targetSync());
 
     // Delete Junction pointing to a missing directory.
     new Directory(y).deleteSync();
     Expect.isFalse(FileSystemEntity.isLinkSync(y));
     Expect.equals(FileSystemEntityType.NOT_FOUND,
                   FileSystemEntity.typeSync(y));
+    Expect.throws(() => new Link(y).targetSync());
 
     new Directory(x).createSync();
     new Link(y).create(x).then((_) {
       Expect.equals(FileSystemEntityType.LINK,
                     FileSystemEntity.typeSync(y, followLinks: false));
       Expect.equals(FileSystemEntityType.DIRECTORY,
                     FileSystemEntity.typeSync(x, followLinks: false));
+      Expect.equals(x, new Link(y).targetSync());
 
       // Delete Junction pointing to an existing directory.
       new Directory(y).deleteSync();
       Expect.equals(FileSystemEntityType.NOT_FOUND,
                     FileSystemEntity.typeSync(y));
       Expect.equals(FileSystemEntityType.NOT_FOUND,
                     FileSystemEntity.typeSync(y, followLinks: false));
       Expect.equals(FileSystemEntityType.DIRECTORY,
                     FileSystemEntity.typeSync(x));
       Expect.equals(FileSystemEntityType.DIRECTORY,
                     FileSystemEntity.typeSync(x, followLinks: false));
+      Expect.throws(() => new Link(y).targetSync());
+
       temp.deleteSync(recursive: true);
     });
   });
 }
 
 
 main() {
   if (Platform.operatingSystem == 'windows') {
     testJunctionTypeDelete();
   }
 }