Use a monotonic clock in the implementation of Timer.

runtime/lib/timer_impl.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.
 
 // Timer heap implemented as a array-based binary heap[0].
 // This allows for O(1) `first`, O(log(n)) `remove`/`removeFirst` and O(log(n))
 // `add`.
 //
 // To ensure the timers are ordered by insertion time, the _Timer class has a
 // `_id` field set when added to the heap.
@@ skipping 154 matching lines @@
                             int milliSeconds,
                             bool repeating) {
     // Negative timeouts are treated as if 0 timeout.
     if (milliSeconds < 0) {
       milliSeconds = 0;
     }
     // Add one because DateTime.now() is assumed to round down
     // to nearest millisecond, not up, so that time + duration is before
     // duration milliseconds from now. Using microsecond timers like
     // Stopwatch allows detecting that the timer fires early.
-    int now = new DateTime.now().millisecondsSinceEpoch;
+    int now = VMLibraryHooks.timerMillisecondClock();
     int wakeupTime = (milliSeconds == 0) ? now : (now + 1 + milliSeconds);
 
     _Timer timer = new _Timer._internal(callback,
                                         wakeupTime,
                                         milliSeconds,
                                         repeating);
     // Enqueue this newly created timer in the appropriate structure and
     // notify if necessary.
     timer._enqueue();
     return timer;
@@ skipping 39 matching lines @@
   }
 
 
   void _advanceWakeupTime() {
     // Recalculate the next wakeup time. For repeating timers with a 0 timeout
     // the next wakeup time is now.
     _id = _nextId();
     if (_milliSeconds > 0) {
       _wakeupTime += _milliSeconds;
     } else {
-      _wakeupTime = new DateTime.now().millisecondsSinceEpoch;
+      _wakeupTime = VMLibraryHooks.timerMillisecondClock();
     }
   }
 
 
   // Adds a timer to the heap or timer list. Timers with the same wakeup time
   // are enqueued in order and notified in FIFO order.
   void _enqueue() {
     if (_milliSeconds == 0) {
       if (_firstZeroTimer == null) {
         _lastZeroTimer = this;
@@ skipping 87 matching lines @@
       // timer are expired. The first zero timer will be dispatched when its
       // corresponding message is delivered.
       var timer;
       while (!_heap.isEmpty && (_heap.first._compareTo(_firstZeroTimer) < 0)) {
         timer = _heap.removeFirst();
         pendingTimers.add(timer);
       }
     } else {
       // Collect pending timers from the timer heap which have expired at this
       // time.
-      var currentTime = new DateTime.now().millisecondsSinceEpoch;
+      var currentTime = VMLibraryHooks.timerMillisecondClock();
       var timer;
       while (!_heap.isEmpty && (_heap.first._wakeupTime <= currentTime)) {
         timer = _heap.removeFirst();
         pendingTimers.add(timer);
       }
     }
     return pendingTimers;
   }
 
 
@@ skipping 109 matching lines @@
       return new _Timer.periodic(milliSeconds, callback);
     }
     return new _Timer(milliSeconds, callback);
   }
 }
 
 
 _setupHooks() {
   VMLibraryHooks.timerFactory = _Timer._factory;
 }