Add back accidentally removed pragma on scheduleMicrotask.

Was removed in a failed merge.

Change-Id: Ie8bd18f434786dbb7a3bc619d0b49565198c8c9c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/182782
Auto-Submit: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Régis Crelier <regis@google.com>
Commit-Queue: Régis Crelier <regis@google.com>
diff --git a/sdk/lib/async/schedule_microtask.dart b/sdk/lib/async/schedule_microtask.dart
index bb6d600..314d474 100644
--- a/sdk/lib/async/schedule_microtask.dart
+++ b/sdk/lib/async/schedule_microtask.dart
@@ -125,6 +125,7 @@
 /// * [The Event Loop and Dart](https://dart.dev/articles/event-loop/):
 /// Learn how Dart handles the event queue and microtask queue, so you can write
 /// better asynchronous code with fewer surprises.
+@pragma('vm:entry-point', 'call')
 void scheduleMicrotask(void Function() callback) {
   _Zone currentZone = Zone._current;
   if (identical(_rootZone, currentZone)) {