Add isActive field on Timer.

sdk/lib/io/timer_impl.dart

Index: sdk/lib/io/timer_impl.dart
diff --git a/sdk/lib/io/timer_impl.dart b/sdk/lib/io/timer_impl.dart
index 73c7cae1c12ccad966449f43d93515a138917c10..42b8a77ad7e8447315a42900f863b155a9ffcd30 100644
--- a/sdk/lib/io/timer_impl.dart
+++ b/sdk/lib/io/timer_impl.dart
@@ -50,6 +50,8 @@ class _Timer extends LinkedListEntry<_Timer> implements Timer {
 
   bool get _repeating => _milliSeconds >= 0;
 
+  bool get _isActive => _timers.contains(this);

[floitsch, 2013/07/01 12:49:43]

contains is a linear operation.
Reuse _callback instead.
It is currently not cleared for single-shot timers, but that's easy to add in
line 148.

[zarah, 2013/07/01 16:15:35]

Done.

+
 
   // Cancels a set timer. The timer is removed from the timer list and if
   // the given timer is the earliest timer the native timer is reset.