Mojo C++ bindings: introduce an optional array to store transferred interface IDs in messages.

mojo/public/cpp/bindings/associated_group_controller.h

 // Copyright 2016 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_CPP_BINDINGS_ASSOCIATED_GROUP_CONTROLLER_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_ASSOCIATED_GROUP_CONTROLLER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 20 matching lines @@
   // locally; while |remote_endpoint| is sent over the message pipe.
   virtual void CreateEndpointHandlePair(
       ScopedInterfaceEndpointHandle* local_endpoint,
       ScopedInterfaceEndpointHandle* remote_endpoint) = 0;
 
   // Creates an interface endpoint handle from a given interface ID. The handle
   // is used locally.
   // Typically, this method is used to (1) create an endpoint handle for the
   // master interface; or (2) create an endpoint handle on receiving an
   // interface ID from the message pipe.
+  //
+  // On failure, the method returns an invalid handle. Usually that is because
+  // the ID has already been used to create a handle.
   virtual ScopedInterfaceEndpointHandle CreateLocalEndpointHandle(
       InterfaceId id) = 0;
 
   // Closes an interface endpoint handle.
   virtual void CloseEndpointHandle(
       InterfaceId id,
       bool is_local,
       const base::Optional<DisconnectReason>& reason) = 0;
 
   // Attaches a client to the specified endpoint to send and receive messages.
@@ skipping 24 matching lines @@
   ScopedInterfaceEndpointHandle CreateScopedInterfaceEndpointHandle(
       InterfaceId id,
       bool is_local);
 
   virtual ~AssociatedGroupController();
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_ASSOCIATED_GROUP_CONTROLLER_H_