Add isActive field on Timer.

sdk/lib/async/zone.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.
 
 part of dart.async;
 
 /**
  * A Zone represents the asynchronous version of a dynamic extent. Asynchronous
  * callbacks are executed in the zone they have been queued in. For example,
  * the callback of a `future.then` is executed in the same zone as the one where
@@ skipping 418 matching lines @@
 
 typedef void _TimerCallback();
 
 /**
  * A [Timer] class that takes zones into account.
  */
 class _ZoneTimer implements Timer {
   final _Zone _zone;
   final _TimerCallback _callback;
   Timer _timer;
-  bool _isDone = false;
 
   _ZoneTimer(this._zone, Duration duration, this._callback) {
     _zone.expectCallback();
     _timer = _createTimer(duration, this._run);
   }
 
   void _run() {
-    _isDone = true;
     _zone.executeCallbackGuarded(_callback);
   }
 
   void cancel() {
-    if (!_isDone) _zone.cancelCallbackExpectation();
-    _isDone = true;
+    if (_timer.isActive) _zone.cancelCallbackExpectation();
     _timer.cancel();
   }
+
+  bool get isActive => _timer.isActive;
 }
 
 typedef void _PeriodicTimerCallback(Timer timer);
 
 /**
  * A [Timer] class for periodic callbacks that takes zones into account.
  */
 class _PeriodicZoneTimer implements Timer {
   final _Zone _zone;
   final _PeriodicTimerCallback _callback;
   Timer _timer;
-  bool _isDone = false;
 
   _PeriodicZoneTimer(this._zone, Duration duration, this._callback) {
     _zone.expectCallback();
     _timer = _createPeriodicTimer(duration, this._run);
   }
 
   void _run(Timer timer) {
     assert(identical(_timer, timer));
     _zone.executePeriodicCallbackGuarded(() { _callback(this); });
   }
 
   void cancel() {
-    if (!_isDone) _zone.cancelCallbackExpectation();
-    _isDone = true;
+    if (_timer.isActive) _zone.cancelCallbackExpectation();
     _timer.cancel();
   }
+
+  bool get isActive => _timer.isActive;
 }
 
 /**
  * Runs [body] in its own zone.
  *
  * If [onError] is non-null the zone is considered an error zone. All uncaught
  * errors, synchronous or asynchronous, in the zone are caught and handled
  * by the callback.
  *
  * The [onDone] handler (if non-null) is invoked when the zone has no more
@@ skipping 56 matching lines @@
   if (onError == null && onDone == null) return body();
   if (onError == null) {
     _WaitForCompletionZone zone =
         new _WaitForCompletionZone(_Zone._current, onDone);
     return zone.runWaitForCompletion(body);
   }
   if (onDone == null) onDone = _nullDoneHandler;
   _CatchErrorsZone zone = new _CatchErrorsZone(_Zone._current, onError, onDone);
   return zone.runWaitForCompletion(body);
 }