Fix some analyzer warnings and hints in pkg/watcher.

pkg/watcher/lib/src/directory_watcher/linux.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.linux;
 
 import 'dart:async';
 import 'dart:io';
 
-import '../directory_watcher.dart';
 import '../utils.dart';
 import '../watch_event.dart';
 import 'resubscribable.dart';
 
 /// Uses the inotify subsystem to watch for filesystem events.
 ///
 /// Inotify doesn't suport recursively watching subdirectories, nor does
 /// [Directory.watch] polyfill that functionality. This class polyfills it
 /// instead.
 ///
@@ skipping 266 matching lines @@
   static const DIRECTORY = const _EntryState._("directory");
 
   const _EntryState._(this._name);
 
   /// Returns [DIRECTORY] if [isDir] is true, and [FILE] otherwise.
   factory _EntryState(bool isDir) =>
       isDir ? _EntryState.DIRECTORY : _EntryState.FILE;
 
   String toString() => _name;
 }