Roll Observatory packages and add a roll script

watcher/lib/src/file_watcher.dart

-// Copyright (c) 2015, 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.file_watcher;
-
-import 'dart:io';
-
-import 'watch_event.dart';
-import '../watcher.dart';
-import 'file_watcher/native.dart';
-import 'file_watcher/polling.dart';
-
-/// Watches a file and emits [WatchEvent]s when the file has changed.
-///
-/// Note that since each watcher only watches a single file, it will only emit
-/// [ChangeType.MODIFY] events, except when the file is deleted at which point
-/// it will emit a single [ChangeType.REMOVE] event and then close the stream.
-///
-/// If the file is deleted and quickly replaced (when a new file is moved in its
-/// place, for example) this will emit a [ChangeTime.MODIFY] event.
-abstract class FileWatcher implements Watcher {
-  /// Creates a new [FileWatcher] monitoring [file].
-  ///
-  /// If a native file watcher is available for this platform, this will use it.
-  /// Otherwise, it will fall back to a [PollingFileWatcher]. Notably, native
-  /// file watching is *not* supported on Windows.
-  ///
-  /// If [pollingDelay] is passed, it specifies the amount of time the watcher
-  /// will pause between successive polls of the directory contents. Making this
-  /// shorter will give more immediate feedback at the expense of doing more IO
-  /// and higher CPU usage. Defaults to one second. Ignored for non-polling
-  /// watchers.
-  factory FileWatcher(String file, {Duration pollingDelay}) {
-    // [File.watch] doesn't work on Windows, but
-    // [FileSystemEntity.isWatchSupported] is still true because directory
-    // watching does work.
-    if (FileSystemEntity.isWatchSupported && !Platform.isWindows) {
-      return new NativeFileWatcher(file);
-    }
-    return new PollingFileWatcher(file, pollingDelay: pollingDelay);
-  }
-}