Stub in more IPC attachment brokering functionality.

ipc/brokerable_attachment.h

 // Copyright 2015 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 IPC_BROKERABLE_ATTACHMENT_H_
 #define IPC_BROKERABLE_ATTACHMENT_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "ipc/ipc_export.h"
 #include "ipc/ipc_message_attachment.h"
 
 namespace IPC {
 
 // This subclass of MessageAttachment requires an AttachmentBroker to be
 // attached to a Chrome IPC message.
 class IPC_EXPORT BrokerableAttachment : public MessageAttachment {
  public:
   // An id uniquely identifies an attachment sent via a broker.
   struct IPC_EXPORT AttachmentId {
     uint32_t nonce[4];
   };
 
+  enum BrokerableType {
+    WIN_HANDLE,
+  };
+
   // The identifier is unique across all Chrome processes.
   AttachmentId GetIdentifier() const;
 
+  // Returns TYPE_BROKERABLE_ATTACHMENT
+  Type GetType() const override;
+
+  virtual BrokerableType GetBrokerableType() const = 0;
+
  protected:
   BrokerableAttachment();
   ~BrokerableAttachment() override;
 
  private:
   // This member uniquely identifies a BrokerableAttachment across all Chrome
   // processes.
-  AttachmentId id_;
+  const AttachmentId id_;
   DISALLOW_COPY_AND_ASSIGN(BrokerableAttachment);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_BROKERABLE_ATTACHMENT_H_