Make attachment broker a subclass of IPC::Listener.

ipc/attachment_broker.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_ATTACHMENT_BROKER_H_
 #define IPC_ATTACHMENT_BROKER_H_
 
 #include "base/macros.h"
 #include "base/process/process_handle.h"
 #include "ipc/brokerable_attachment.h"
 #include "ipc/ipc_export.h"
+#include "ipc/ipc_listener.h"
 
 namespace IPC {
 
 class AttachmentBroker;
 // Classes that inherit from this abstract base class are capable of
 // communicating with a broker to send and receive attachments to Chrome IPC
 // messages.
 class IPC_EXPORT SupportsAttachmentBrokering {
  public:
   // Returns an AttachmentBroker used to broker attachments of IPC messages to
   // other processes. There must be exactly one AttachmentBroker per process.
   virtual AttachmentBroker* GetAttachmentBroker() = 0;
 };
 
 // Responsible for brokering attachments to Chrome IPC messages. On platforms
 // that support attachment brokering, every IPC channel should have a reference
 // to a AttachmentBroker.
-class IPC_EXPORT AttachmentBroker {
+class IPC_EXPORT AttachmentBroker : public Listener {
  public:
   AttachmentBroker() {}
-  virtual ~AttachmentBroker() {}
+  ~AttachmentBroker() override {}
 
   // Sends |attachment| to |destination_process|. The implementation uses an
   // IPC::Channel to communicate with the broker process. This may be the same
   // IPC::Channel that is requesting the brokering of an attachment.
   // Returns true on success and false otherwise.
   virtual bool SendAttachmentToProcess(const BrokerableAttachment* attachment,
                                        base::ProcessId destination_process) = 0;
 
   // Returns whether the attachment was available. If the attachment was
   // available, populates the output parameter |attachment|. The caller then
   // becomes the owner of |attachment|.
   virtual bool GetAttachmentWithId(BrokerableAttachment::AttachmentId id,
                                    BrokerableAttachment* attachment) = 0;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(AttachmentBroker);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_H_