Make the root zone's schduleMicrotask and create[Periodic]Timer bind the callback.

sdk/lib/async/timer.dart

Index: sdk/lib/async/timer.dart
diff --git a/sdk/lib/async/timer.dart b/sdk/lib/async/timer.dart
index 0fb0ceae26ff1972abd05307cf780eff752556d8..8b2b115149f3c02aa904f2a35b9eb3c4c7289faa 100644
--- a/sdk/lib/async/timer.dart
+++ b/sdk/lib/async/timer.dart
@@ -60,7 +60,7 @@ abstract class Timer {
    * canceled with the [cancel] function.
    */
   factory Timer.periodic(Duration duration,
-                                  void callback(Timer timer)) {
+                         void callback(Timer timer)) {
     if (Zone.current == Zone.ROOT) {
       // No need to bind the callback. We know that the root's timer will
       // be invoked in the root zone.