Mojo: Refactor some message pipe stuff.

mojo/system/message_pipe.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_SYSTEM_MESSAGE_PIPE_H_
 #define MOJO_SYSTEM_MESSAGE_PIPE_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 48 matching lines @@
                          MojoReadMessageFlags flags);
   MojoResult AddWaiter(unsigned port,
                        Waiter* waiter,
                        MojoWaitFlags flags,
                        MojoResult wake_result);
   void RemoveWaiter(unsigned port, Waiter* waiter);
 
   // This is used internally by |WriteMessage()| and by |Channel| to enqueue
   // messages (typically to a |LocalMessagePipeEndpoint|). Unlike
   // |WriteMessage()|, |port| is the *destination* port. Takes ownership of
-  // |message|.
+  // |message|. |dispatchers| should be non-null only if it's nonempty.
   MojoResult EnqueueMessage(unsigned port,
                             MessageInTransit* message,
                             const std::vector<Dispatcher*>* dispatchers);
 
   // These are used by |Channel|.
   void Attach(unsigned port,
               scoped_refptr<Channel> channel,
               MessageInTransit::EndpointId local_id);
   void Run(unsigned port, MessageInTransit::EndpointId remote_id);
 
  private:
   friend class base::RefCountedThreadSafe<MessagePipe>;
   virtual ~MessagePipe();
 
   // Used by |EnqueueMessage()| to handle control messages that are actually
   // meant for us.
   MojoResult HandleControlMessage(unsigned port, MessageInTransit* message);
 
   base::Lock lock_;  // Protects the following members.
   scoped_ptr<MessagePipeEndpoint> endpoints_[2];
 
   DISALLOW_COPY_AND_ASSIGN(MessagePipe);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_MESSAGE_PIPE_H_