dart:io | Add asynchronous versions of the methods of FileSystemEntity and Link.

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 "package:expect/expect.dart";
 import "dart:io";
 import "dart:isolate";
 
 
 createLink(String dst, String link, void callback()) {
@@ skipping 221 matching lines @@
           Expect.equals(0, dirs.length);
           Expect.equals(0, errors.length);
           temp.deleteSync(recursive: true);
           keepAlive.close();
         });
   });
 }
 
 
 main() {
-  testFileExistsCreate();
-  testFileDelete();
-  testFileWriteRead();
-  testDirectoryExistsCreate();
-  testDirectoryDelete();
-  testDirectoryListing();
-  testDirectoryListingBrokenLink();
+  // Links on Windows are tested by windows_file_system_[async_]links_test.
+  if (Platform.operatingSystem != 'windows') {
+    testFileExistsCreate();
+    testFileDelete();
+    testFileWriteRead();
+    testDirectoryExistsCreate();
+    testDirectoryDelete();
+    testDirectoryListing();
+    testDirectoryListingBrokenLink();
+  }
 }