Add Dart_PostPriority function to dart_api, and use it in runAsync to schedule immediate events in …

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 680476e543583d3dd6e116dafc14bdf22707cf94..9daf794ed040ce4abd3c8bcc747cbf8a5fa587de 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1057,6 +1057,19 @@ DART_EXPORT bool Dart_Post(Dart_Port port_id, Dart_Handle handle) {
 }
 
 
+DART_EXPORT bool Dart_PostPriority(Dart_Port port_id, Dart_Handle handle) {
+  Isolate* isolate = Isolate::Current();
+  DARTSCOPE(isolate);
+  const Object& object = Object::Handle(isolate, Api::UnwrapHandle(handle));
+  uint8_t* data = NULL;
+  MessageWriter writer(&data, &allocator);
+  writer.WriteMessage(object);
+  intptr_t len = writer.BytesWritten();
+  return PortMap::PostMessage(new Message(
+      port_id, Message::kIllegalPort, data, len, Message::kFirstPriority));
+}
+
+
 DART_EXPORT Dart_Handle Dart_NewSendPort(Dart_Port port_id) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);