Close file watcher when target is deleted.

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";
 
@@ skipping 93 matching lines @@
     }
   }, onError: (e) {
     dir.deleteSync(recursive: true);
     throw e;
   });
 
   file.deleteSync();
 }
 
 
+void testWatchDeleteDir() {
+  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: () {
+    asyncEnd();
+  });
+
+  dir.deleteSync();
+}
+
+
 void testWatchOnlyModifyFile() {
   var dir = Directory.systemTemp.createTempSync('dart_file_system_watcher');
   var file = new File(dir.path + '/file');
 
   var watcher = dir.watch(events: FileSystemEvent.MODIFY);
 
   asyncStart();
   var sub;
   sub = watcher.listen((event) {
     Expect.isTrue(event is FileSystemModifyEvent);
@@ skipping 113 matching lines @@
   });
 }
 
 
 void main() {
   if (!FileSystemEntity.isWatchSupported) return;
   testWatchCreateFile();
   testWatchModifyFile();
   testWatchMoveFile();
   testWatchDeleteFile();
+  testWatchDeleteDir();
   testWatchOnlyModifyFile();
   testMultipleEvents();
   testWatchNonRecursive();
 }