Revert https://code.google.com/p/dart/source/detail?r=597

vm/message_queue.cc

Index: vm/message_queue.cc
===================================================================
--- vm/message_queue.cc	(revision 621)
+++ vm/message_queue.cc	(working copy)
@@ -40,13 +40,9 @@
 PortMessage* MessageQueue::Dequeue(int64_t millis) {
   MonitorLocker ml(&monitor_);
   PortMessage* result = head_;
-  // Wait may wake up prematurely, so we need to loop until result != NULL
-  while (result == NULL) {
+  if (result == NULL) {
     ml.Wait(millis);
     result = head_;
-    // If there's a time-out the caller must check for NULL anyway.
-    if (0 < millis)
-      break;
   }
   if (result != NULL) {
     head_ = result->next_;