Add factory-method for scheduleMicrotask, as well as a (failing) test.

sdk/lib/async/schedule_microtask.dart

Index: sdk/lib/async/schedule_microtask.dart
diff --git a/sdk/lib/async/event_loop.dart b/sdk/lib/async/schedule_microtask.dart
similarity index 90%
rename from sdk/lib/async/event_loop.dart
rename to sdk/lib/async/schedule_microtask.dart
index 42c25ecdbce26ea8f2741eb05c1e497bed612445..c732874be437eed5a1a6af41c28f2af4dd27c873 100644
--- a/sdk/lib/async/event_loop.dart
+++ b/sdk/lib/async/schedule_microtask.dart
@@ -17,7 +17,7 @@ void _asyncRunCallback() {
     try {
       callback();
     } catch (e) {
-      _AsyncRun._enqueueImmediate(_asyncRunCallback);
+      _AsyncRun._scheduleImmediate(_asyncRunCallback);
       rethrow;
     }
   }
@@ -30,7 +30,7 @@ void _scheduleAsyncCallback(callback) {
   // same Timer callback.
   _asyncCallbacks.add(callback);
   if (!_callbacksAreEnqueued) {
-    _AsyncRun._enqueueImmediate(_asyncRunCallback);
+    _AsyncRun._scheduleImmediate(_asyncRunCallback);
     _callbacksAreEnqueued = true;
   }
 }
@@ -74,6 +74,6 @@ void runAsync(void callback()) {
 }
 
 class _AsyncRun {
-  /** Enqueues the given callback before any other event in the event-loop. */
-  external static void _enqueueImmediate(void callback());
+  /** Schedule the given callback before any other event in the event-loop. */
+  external static void _scheduleImmediate(void callback());
 }