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

tests/standalone/standalone.status

 # 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.
 
 package/invalid_uri_test: Fail, OK # Fails intentionally
 
 [ $runtime == vm ]
 # Fails because checked-in dart executable is not up to date.
 io/test_runner_test: Fail
 # Fails because checked-in dart executable is not up to date.
@@ skipping 29 matching lines @@
 # that are running an earlier version of MacOS. The issue is that the
 # old version of MacOS does not expand the precomposed utf-8 it gets
 # from the VM before comparing it to the decomposed utf-8 used for the
 # file system.
 io/file_non_ascii_sync_test: Pass, Fail
 io/file_non_ascii_test: Pass, Fail
 io/directory_non_ascii_sync_test: Pass, Fail
 io/directory_non_ascii_test: Pass, Fail
 io/process_non_ascii_test: Pass, Fail
 
-[ $runtime == vm && $system == windows ]
-io/file_system_links_test: Skip  # No links on Windows.
-io/file_read_special_device_test: Skip  # No special unix devices on Windows.
-
 [ $compiler == none && $runtime == drt ]
 typed_data_isolate_test: Skip # This test uses dart:io
 io/*: Skip # Don't run tests using dart:io in the browser
 crypto/*: Skip # Don't run tests using dart:io in the browser
 package/*: Skip # Do not run those in Dartium.
 debugger/*: Skip # Do not run standalone debugger tests in browser.
 
 [ $compiler == dartc ]
 
 # package test issue 7392
@@ skipping 59 matching lines @@
 *: Skip
 
 [ $arch == simarm ]
 *: Skip
 
 [ $arch == mips ]
 *: Skip
 
 [ $arch == simmips ]
 *: Skip