Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/watcher/lib/src/file_watcher/polling.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.polling;
+
+import 'dart:async';
+import 'dart:io';
+
+import '../file_watcher.dart';
+import '../resubscribable.dart';
+import '../stat.dart';
+import '../watch_event.dart';
+
+/// Periodically polls a file for changes.
+class PollingFileWatcher extends ResubscribableWatcher implements FileWatcher {
+  PollingFileWatcher(String path, {Duration pollingDelay})
+      : super(path, () {
+        return new _PollingFileWatcher(path,
+            pollingDelay != null ? pollingDelay : new Duration(seconds: 1));
+      });
+}
+
+class _PollingFileWatcher implements FileWatcher, ManuallyClosedWatcher {
+  final String path;
+
+  Stream<WatchEvent> get events => _eventsController.stream;
+  final _eventsController = new StreamController<WatchEvent>.broadcast();
+
+  bool get isReady => _readyCompleter.isCompleted;
+
+  Future get ready => _readyCompleter.future;
+  final _readyCompleter = new Completer();
+
+  /// The timer that controls polling.
+  Timer _timer;
+
+  /// The previous modification time of the file.
+  ///
+  /// Used to tell when the file was modified. This is `null` before the file's
+  /// mtime has first been checked.
+  DateTime _lastModified;
+
+  _PollingFileWatcher(this.path, Duration pollingDelay) {
+    _timer = new Timer.periodic(pollingDelay, (_) => _poll());
+    _poll();
+  }
+
+  /// Checks the mtime of the file and whether it's been removed.
+  Future _poll() async {
+    // We don't mark the file as removed if this is the first poll (indicated by
+    // [_lastModified] being null). Instead, below we forward the dart:io error
+    // that comes from trying to read the mtime below.
+    var pathExists = await new File(path).exists();
+    if (_eventsController.isClosed) return;
+
+    if (_lastModified != null && !pathExists) {
+      _eventsController.add(new WatchEvent(ChangeType.REMOVE, path));
+      close();
+      return;
+    }
+
+    var modified;
+    try {
+      try {
+        modified = await getModificationTime(path);
+      } finally {
+        if (_eventsController.isClosed) return;
+      }
+    } on FileSystemException catch (error, stackTrace) {
+      _eventsController.addError(error, stackTrace);
+      close();
+      return;
+    }
+
+    if (_lastModified == modified) return;
+
+    if (_lastModified == null) {
+      // If this is the first poll, don't emit an event, just set the last mtime
+      // and complete the completer.
+      _lastModified = modified;
+      _readyCompleter.complete();
+    } else {
+      _lastModified = modified;
+      _eventsController.add(new WatchEvent(ChangeType.MODIFY, path));
+    }
+  }
+
+  void close() {
+    _timer.cancel();
+    _eventsController.close();
+  }
+}