If a new timer is the last timer to time out, don't run through the entire list of timers.

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 f03b6180e5e17c2c3c1788fb387e46da667e4565..a3eb9529a360a177f4e13de35d6f599afc4a1095 100644
--- a/sdk/lib/io/timer_impl.dart
+++ b/sdk/lib/io/timer_impl.dart
@@ -79,6 +79,12 @@ class _Timer extends LinkedListEntry<_Timer> implements Timer {
   // enqueued in order and notified in FIFO order.
   void _addTimerToList() {
     _Timer entry = _timers.isEmpty ? null : _timers.first;
+    // If timer is last, add to end.
+    if (entry == null || _timers.last._wakeupTime <= _wakeupTime) {
+      _timers.add(this);
+      return;
+    }
+    // Otherwise scan through and find the right position.
     while (entry != null) {
       if (_wakeupTime < entry._wakeupTime) {
         entry.insertBefore(this);