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

runtime/lib/event_loop_patch.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.
 
 patch class _AsyncRun {
   /* patch */ static void _enqueueImmediate(void callback()) {
-    // TODO(9001): don't use the Timer to enqueue the immediate callback.
-    _createTimer(Duration.ZERO, callback);
+    if (_EnqueueImmediateFactory._factory == null) {
+      // TODO(9001): don't default to using the Timer to enqueue the immediate
+      //             callback.
+      _createTimer(Duration.ZERO, callback);
+      return;
+    }
+    _EnqueueImmediateFactory._factory(callback);
   }
 }
+
+typedef void _EnqueueImmediateFactoryClosure(void callback());
+
+class _EnqueueImmediateFactory {

[floitsch, 2013/10/11 09:35:37]

I think factory is the wrong name.
For timers it was called "factory" because it was constructing Timer objects.
That's not the case here.

_microtaskScheduler outside a class?
void _setMicrotaskScheduler(...) ?

[Anders Johnsen, 2013/10/14 10:15:10]

Done.

+  static _EnqueueImmediateFactoryClosure _factory;
+}
+
+void _setEnqueueImmediateFactoryClosure(
+    _EnqueueImmediateFactoryClosure closure) {
+  _EnqueueImmediateFactory._factory = closure;
+}