Refactor isolate startup code in preparation for making isolate spawning more truly non-blocking.

runtime/vm/message_handler.h

 // 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.
 
 #ifndef VM_MESSAGE_HANDLER_H_
 #define VM_MESSAGE_HANDLER_H_
 
 #include "vm/isolate.h"
 #include "vm/message.h"
 #include "vm/thread.h"
@@ skipping 36 matching lines @@
   //
   // Returns true on success.
   bool HandleNextMessage();
 
   // Handles any OOB messages for this message handler.  Can be used
   // even if the message handler is running on the thread pool.
   //
   // Returns true on success.
   bool HandleOOBMessages();
 
-  // The number of opened control ports is determined whether the isolate has
-  // live ports. An isolate is considered not having any live ports if only
-  // control ports are open.
-  // Usually either 0 or 1.
-  void increment_control_ports();
-  void decrement_control_ports();
-
   // A message handler tracks how many live ports it has.
-  bool HasLivePorts() const { return live_ports_ > control_ports_; }
+  bool HasLivePorts() const { return live_ports_ > 0; }
 
   intptr_t live_ports() const {
     return live_ports_;
   }
 
-  intptr_t control_ports() const {
-    return control_ports_;
-  }
-
   bool paused() const { return paused_ > 0; }
 
   void increment_paused() { paused_++; }
   void decrement_paused() { ASSERT(paused_ > 0); paused_--; }
 
   bool pause_on_start() const {
     return pause_on_start_;
   }
 
   void set_pause_on_start(bool pause_on_start) {
@@ skipping 76 matching lines @@
   // messages from the queue_.
   Message* DequeueMessage(Message::Priority min_priority);
 
   // Handles any pending messages.
   bool HandleMessages(bool allow_normal_messages,
                       bool allow_multiple_normal_messages);
 
   Monitor monitor_;  // Protects all fields in MessageHandler.
   MessageQueue* queue_;
   MessageQueue* oob_queue_;
-  intptr_t control_ports_;  // The number of open control ports usually 0 or 1.
   intptr_t live_ports_;  // The number of open ports, including control ports.
   intptr_t paused_;  // The number of pause messages received.
   bool pause_on_start_;
   bool pause_on_exit_;
   bool paused_on_exit_;
   ThreadPool* pool_;
   ThreadPool::Task* task_;
   StartCallback start_callback_;
   EndCallback end_callback_;
   CallbackData callback_data_;
 
   DISALLOW_COPY_AND_ASSIGN(MessageHandler);
 };
 
 }  // namespace dart
 
 #endif  // VM_MESSAGE_HANDLER_H_