Mojo: More plumbing to support sending handles over MessagePipes.

mojo/system/dispatcher.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_DISPATCHER_H_
 #define MOJO_SYSTEM_DISPATCHER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 24 matching lines @@
   // prevents the various |...ImplNoLock()|s from releasing the lock as soon as
   // possible. If this becomes an issue, we can rethink this.
   MojoResult Close();
   // |dispatchers| may be non-null if and only if there are handles to be
   // written, in which case this will be called with all the dispatchers' locks
   // held. On success, all the dispatchers must have been moved to a closed
   // state; on failure, they should remain in their original state.
   MojoResult WriteMessage(const void* bytes, uint32_t num_bytes,
                           const std::vector<Dispatcher*>* dispatchers,
                           MojoWriteMessageFlags flags);
-  // |dispatchers| must be non-null if |max_num_dispatchers| is nonzero. On
-  // success, it will be set to the dispatchers to be received (and assigned
-  // handles) as part of the message.
+  // |dispatchers| must be non-null but empty, if |max_num_dispatchers| is
+  // nonzero. On success, it will be set to the dispatchers to be received (and
+  // assigned handles) as part of the message.
   MojoResult ReadMessage(
       void* bytes, uint32_t* num_bytes,
       uint32_t max_num_dispatchers,
       std::vector<scoped_refptr<Dispatcher> >* dispatchers,
       MojoReadMessageFlags flags);
 
   // Adds a waiter to this dispatcher. The waiter will be woken up when this
   // object changes state to satisfy |flags| with result |wake_result| (which
   // must be >= 0, i.e., a success status). It will also be woken up when it
   // becomes impossible for the object to ever satisfy |flags| with a suitable
@@ skipping 53 matching lines @@
   mutable base::Lock lock_;
   bool is_closed_;
 
   DISALLOW_COPY_AND_ASSIGN(Dispatcher);
 };
 
 }  // namespace system
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_DISPATCHER_H_