Add better handle tracking, and optimize Connector::Accept.

mojo/public/bindings/lib/message_queue.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_BINDINGS_LIB_MESSAGE_QUEUE_H_
 #define MOJO_PUBLIC_BINDINGS_LIB_MESSAGE_QUEUE_H_
 
 #include <queue>
 
 #include "mojo/public/system/macros.h"
 
 namespace mojo {
 
 class Message;
 
 // A queue for Message objects.
 class MessageQueue {
  public:
   MessageQueue();
   ~MessageQueue();
 
   bool IsEmpty() const;
-  const Message* Peek() const;
+  Message* Peek();
 
   // This method transfers ownership of |message->data| and |message->handles|
   // to the message queue, resetting |message| in the process.
   void Push(Message* message);
 
   // Removes the next message from the queue, transferring ownership of its
   // data and handles to the given |message|.
   void Pop(Message* message);
 
   // Removes the next message from the queue, discarding its data and handles.
   // This is meant to be used in conjunction with |Peek|.
   void Pop();
 
  private:
   std::queue<Message*> queue_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(MessageQueue);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_BINDINGS_LIB_MESSAGE_QUEUE_H_