Modernize the package's style.

lib/src/restartable_timer.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 async.restartable_timer;
-
 import 'dart:async';
 
 /// A non-periodic timer that can be restarted any number of times.
 ///
 /// Once restarted (via [reset]), the timer counts down from its original
 /// duration again.
 class RestartableTimer implements Timer {
   /// The duration of the timer.
   final Duration _duration;
 
@@ skipping 22 matching lines @@
   /// This restarts the timer even if it has already fired or has been canceled.
   void reset() {
     _timer.cancel();
     _timer = new Timer(_duration, _callback);
   }
 
   void cancel() {
     _timer.cancel();
   }
 }