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

tests/standalone/io/link_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";
 
 // Test the dart:io Link class.
 
 testCreateSync() {
@@ skipping 10 matching lines @@
   Expect.equals(FileSystemEntityType.LINK,
                 FileSystemEntity.typeSync(link, followLinks: false));
   Expect.equals(FileSystemEntityType.DIRECTORY,
                 FileSystemEntity.typeSync(target, followLinks: false));
   Expect.isTrue(FileSystemEntity.isLinkSync(link));
   Expect.isFalse(FileSystemEntity.isLinkSync(target));
   Expect.isTrue(new Directory(link).existsSync());
   Expect.isTrue(new Directory(target).existsSync());
   Expect.isTrue(new Link(link).existsSync());
   Expect.isFalse(new Link(target).existsSync());
+  Expect.equals(target, new Link(link).targetSync());
 
   String createdThroughLink =
       base.append('link/createdThroughLink').toNativePath();
   String createdDirectly = base.append('target/createdDirectly').toNativePath();
   new Directory(createdThroughLink).createSync();
   new Directory(createdDirectly).createSync();
   Expect.isTrue(new Directory(createdThroughLink).existsSync());
   Expect.isTrue(new Directory(createdDirectly).existsSync());
   Expect.isTrue(new Directory.fromPath(base.append('link/createdDirectly'))
                 .existsSync());
   Expect.isTrue(new Directory.fromPath(base.append('target/createdThroughLink'))
                 .existsSync());
   Expect.equals(FileSystemEntityType.DIRECTORY,
                 FileSystemEntity.typeSync(createdThroughLink,
                                           followLinks: false));
   Expect.equals(FileSystemEntityType.DIRECTORY,
                 FileSystemEntity.typeSync(createdDirectly, followLinks: false));
 
   new Directory.fromPath(base).deleteSync(recursive: true);
 }
 
 
 main() {
   testCreateSync();
 }