Add first version of runAsync.

sdk/lib/_internal/compiler/implementation/lib/async_patch.dart

Index: sdk/lib/_internal/compiler/implementation/lib/async_patch.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/async_patch.dart b/sdk/lib/_internal/compiler/implementation/lib/async_patch.dart
index ade4c9955cffabd6c993b61c16995070b429e3f8..c73dcc749dbf5c592689e2c9096d997cf68bfc71 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/async_patch.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/async_patch.dart
@@ -21,6 +21,13 @@ patch class Timer {
   }
 }
 
+patch class _AsyncRun {
+  patch static void _enqueueImmediate(void callback()) {
+    // TODO(floitsch): don't use the Timer to enqueue the immediate callback.
+    Timer.run(callback);
+  }
+}
+
 patch class DeferredLibrary {
   patch Future<bool> load() {
     return _load(libraryName, uri);