Use a monotonic clock in the implementation of Timer.

runtime/lib/internal_patch.dart

Index: runtime/lib/internal_patch.dart
diff --git a/runtime/lib/internal_patch.dart b/runtime/lib/internal_patch.dart
index 8e955061138b462d53aeeb43b91db4e9ccd9c7f6..0989076ed4dc023132fb4b366051593bc2a0ad49 100644
--- a/runtime/lib/internal_patch.dart
+++ b/runtime/lib/internal_patch.dart
@@ -11,6 +11,8 @@ patch List makeFixedListUnmodifiable(List fixedLengthList)
 class VMLibraryHooks {
   // Example: "dart:isolate _Timer._factory"
   static var timerFactory;
+  // Example: "dart:io _EventHandler._timerMillisecondClock"

[zra, 2015/12/10 22:53:46]

Other than the call site, this is the only place it is documented how this field
should be populated by the embedder. Maybe a little more guidance here would be
appropriate. Maybe just a function type like () -> int would be enough.

[rmacnak, 2015/12/11 18:39:40]

Added.

Noting that eventHandlerSendData has a far more complicated undocumented API.

+  static var timerMillisecondClock;
   // Example: "dart:io _EventHandler._sendData"
   static var eventHandlerSendData;
   // Implementation of Resource.readAsBytes.