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

tests/standalone/io/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";
 
 
 createLink(String dst, String link, void callback()) {
   new Link(link).create(dst).then((_) => callback());
 }
 
 
 testFileExistsCreate() {
   var temp = new Directory('').createTempSync();
   var x = '${temp.path}${Platform.pathSeparator}x';
   var y = '${temp.path}${Platform.pathSeparator}y';
   createLink(x, y, () {
     Expect.isFalse(new File(y).existsSync());
     Expect.isFalse(new File(x).existsSync());
     Expect.isTrue(FileSystemEntity.isLinkSync(y));
     Expect.isFalse(FileSystemEntity.isLinkSync(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());
 
     new File(y).createSync();
     Expect.isTrue(new File(y).existsSync());
     Expect.isTrue(new File(x).existsSync());
     Expect.isTrue(FileSystemEntity.isLinkSync(y));
     Expect.isFalse(FileSystemEntity.isLinkSync(x));
     Expect.isTrue(FileSystemEntity.isFileSync(y));
     Expect.isTrue(FileSystemEntity.isFileSync(x));
     Expect.equals(FileSystemEntityType.FILE, FileSystemEntity.typeSync(y));
     Expect.equals(FileSystemEntityType.FILE, FileSystemEntity.typeSync(x));
     Expect.equals(FileSystemEntityType.LINK,
                   FileSystemEntity.typeSync(y, followLinks: false));
     Expect.equals(FileSystemEntityType.FILE,
                   FileSystemEntity.typeSync(x, followLinks: false));
+    Expect.equals(x, new Link(y).targetSync());
+
     new File(x).deleteSync();
     new Directory(x).createSync();
     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());
+
     new File(y).deleteSync();
     Expect.isFalse(FileSystemEntity.isLinkSync(y));
     Expect.isFalse(FileSystemEntity.isLinkSync(x));
     Expect.equals(FileSystemEntityType.NOT_FOUND, FileSystemEntity.typeSync(y));
     Expect.equals(FileSystemEntityType.DIRECTORY, FileSystemEntity.typeSync(x));
+    Expect.throws(() => new Link(y).targetSync());
 
     temp.deleteSync(recursive: true);
   });
 }
 
 
 testFileDelete() {
   var temp = new Directory('').createTempSync();
   var x = '${temp.path}${Platform.pathSeparator}x';
   var y = '${temp.path}${Platform.pathSeparator}y';
@@ skipping 160 matching lines @@
 
 main() {
   testFileExistsCreate();
   testFileDelete();
   testFileWriteRead();
   testDirectoryExistsCreate();
   testDirectoryDelete();
   testDirectoryListing();
   testDirectoryListingBrokenLink();
 }