Fix file-system-entity watching on Windows.

tests/standalone/io/file_system_watcher_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:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 import "package:path/path.dart";
@@ skipping 121 matching lines @@
   }, onError: (e) {
     dir.deleteSync(recursive: true);
     throw e;
   });
 
   file.deleteSync();
 }
 
 
 void testWatchDeleteDir() {
+  // Windows keeps the directory handle open, even though it's deleted. It'll
+  // be flushed completely, once the watcher is closed as well.
+  if (Platform.isWindows) return;
   var dir = Directory.systemTemp.createTempSync('dart_file_system_watcher');
   var watcher = dir.watch(events: 0);
 
   asyncStart();
   var sub;
   sub = watcher.listen((event) {
     if (event is FileSystemDeleteEvent) {
       Expect.isTrue(event.path == dir.path);
     }
   }, onDone: () {
@@ skipping 151 matching lines @@
   testWatchCreateDir();
   testWatchModifyFile();
   testWatchMoveFile();
   testWatchDeleteFile();
   testWatchDeleteDir();
   testWatchOnlyModifyFile();
   testMultipleEvents();
   testWatchNonRecursive();
   testWatchNonExisting();
 }