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

runtime/vm/message.cc

 // Copyright (c) 2011, 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.
 
 #include "vm/message.h"
 
 namespace dart {
 
 MessageQueue::MessageQueue() {
   head_ = NULL;
@@ skipping 11 matching lines @@
 void MessageQueue::Enqueue(Message* msg) {
   // Make sure messages are not reused.
   ASSERT(msg->next_ == NULL);
   if (head_ == NULL) {
     // Only element in the queue.
     ASSERT(tail_ == NULL);
     head_ = msg;
     tail_ = msg;
   } else {
     ASSERT(tail_ != NULL);
-    // Append at the tail.
-    tail_->next_ = msg;
-    tail_ = msg;
+    if (msg->priority() == Message::kFirstPriority) {
+      // Set as head element in the queue.
+      msg->next_ = head_;
+      head_ = msg;
+    } else {
+      // Append at the tail.
+      tail_->next_ = msg;
+      tail_ = msg;
+    }
   }
 }
 
 
 Message* MessageQueue::Dequeue() {
   Message* result = head_;
   if (result != NULL) {
     head_ = result->next_;
     // The following update to tail_ is not strictly needed.
     if (head_ == NULL) {
@@ skipping 14 matching lines @@
   tail_ = NULL;
   while (cur != NULL) {
     Message* next = cur->next_;
     delete cur;
     cur = next;
   }
 }
 
 
 }  // namespace dart