pkg: analysis aided cleanup

pkg/watcher/lib/src/directory_watcher.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.
 
 library watcher.directory_watcher;
 
 import 'dart:async';
-import 'dart:collection';
 import 'dart:io';
 
 import 'package:crypto/crypto.dart';
 
 import 'async_queue.dart';
 import 'stat.dart';
 import 'watch_event.dart';
 
 /// Watches the contents of a directory and emits [WatchEvent]s when something
 /// in the directory has changed.
@@ skipping 240 matching lines @@
 
 class _FileStatus {
   /// The last time the file was modified.
   DateTime modified;
 
   /// The SHA-1 hash of the contents of the file.
   List<int> hash;
 
   _FileStatus(this.modified, this.hash);
 }