Optimize the message queue for many active ports with few messages.

runtime/vm/message_handler.cc

Index: runtime/vm/message_handler.cc
diff --git a/runtime/vm/message_handler.cc b/runtime/vm/message_handler.cc
index 2727eac008468bc0392a31702063088a4bf8bd84..a3e2170486ac6915b5494ed3b7cf8714abd9a662 100644
--- a/runtime/vm/message_handler.cc
+++ b/runtime/vm/message_handler.cc
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/message_handler.h"
+#include "vm/port.h"
 #include "vm/dart.h"
 
 namespace dart {
@@ -150,9 +151,7 @@ bool MessageHandler::HandleMessages(bool allow_normal_messages,
     monitor_.Exit();
     Message::Priority saved_priority = message->priority();
     result = HandleMessage(message);
-    // ASSERT(Isolate::Current() == NULL);
     monitor_.Enter();
-
     if (!result) {
       // If we hit an error, we're done processing messages.
       break;
@@ -238,8 +237,6 @@ void MessageHandler::ClosePort(Dart_Port port) {
               "\tport:       %"Pd64"\n",
               name(), port);
   }
-  queue_->Flush(port);
-  oob_queue_->Flush(port);
 }
 
 
@@ -250,8 +247,8 @@ void MessageHandler::CloseAllPorts() {
               "\thandler:    %s\n",
               name());
   }
-  queue_->FlushAll();
-  oob_queue_->FlushAll();
+  queue_->Clear();
+  oob_queue_->Clear();
 }