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

tests/standalone/io/windows_file_system_links_test.dart

Index: tests/standalone/io/windows_file_system_links_test.dart
diff --git a/tests/standalone/io/windows_file_system_links_test.dart b/tests/standalone/io/windows_file_system_links_test.dart
index a458a5f9e4095ed2823175ec0ce6518855b57b3f..f161b0e12aea5945dce03cb85b4c3bc0e929dace 100644
--- a/tests/standalone/io/windows_file_system_links_test.dart
+++ b/tests/standalone/io/windows_file_system_links_test.dart
@@ -26,6 +26,8 @@ testJunctionTypeDelete() {
                   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());
@@ -42,12 +44,14 @@ testJunctionTypeDelete() {
                   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((_) {
@@ -55,6 +59,7 @@ testJunctionTypeDelete() {
                     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();
@@ -66,6 +71,8 @@ testJunctionTypeDelete() {
                     FileSystemEntity.typeSync(x));
       Expect.equals(FileSystemEntityType.DIRECTORY,
                     FileSystemEntity.typeSync(x, followLinks: false));
+      Expect.throws(() => new Link(y).targetSync());
+
       temp.deleteSync(recursive: true);
     });
   });