Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/watcher/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:io';
+
+import 'watch_event.dart';
+import 'directory_watcher/linux.dart';
+import 'directory_watcher/mac_os.dart';
+import 'directory_watcher/windows.dart';
+import 'directory_watcher/polling.dart';
+
+/// Watches the contents of a directory and emits [WatchEvent]s when something
+/// in the directory has changed.
+abstract class DirectoryWatcher {
+  /// The directory whose contents are being monitored.
+  String get directory;
+
+  /// The broadcast [Stream] of events that have occurred to files in
+  /// [directory].
+  ///
+  /// Changes will only be monitored while this stream has subscribers. Any
+  /// file changes that occur during periods when there are no subscribers
+  /// will not be reported the next time a subscriber is added.
+  Stream<WatchEvent> get events;
+
+  /// Whether the watcher is initialized and watching for file changes.
+  ///
+  /// This is true if and only if [ready] is complete.
+  bool get isReady;
+
+  /// A [Future] that completes when the watcher is initialized and watching
+  /// for file changes.
+  ///
+  /// If the watcher is not currently monitoring the directory (because there
+  /// are no subscribers to [events]), this returns a future that isn't
+  /// complete yet. It will complete when a subscriber starts listening and
+  /// the watcher finishes any initialization work it needs to do.
+  ///
+  /// If the watcher is already monitoring, this returns an already complete
+  /// future.
+  Future get ready;
+
+  /// Creates a new [DirectoryWatcher] monitoring [directory].
+  ///
+  /// If a native directory watcher is available for this platform, this will
+  /// use it. Otherwise, it will fall back to a [PollingDirectoryWatcher].
+  ///
+  /// 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 DirectoryWatcher(String directory, {Duration pollingDelay}) {
+    if (FileSystemEntity.isWatchSupported) {
+      if (Platform.isLinux) return new LinuxDirectoryWatcher(directory);
+      if (Platform.isMacOS) return new MacOSDirectoryWatcher(directory);
+      if (Platform.isWindows) return new WindowsDirectoryWatcher(directory);
+    }
+    return new PollingDirectoryWatcher(directory, pollingDelay: pollingDelay);
+  }
+}