Make attachment broker a subclass of IPC::Listener.

ipc/handle_attachment_win.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_HANDLE_ATTACHMENT_WIN_H_
 #define IPC_HANDLE_ATTACHMENT_WIN_H_
 
 #include <stdint.h>
 
 #include "base/process/process_handle.h"
@@ skipping 13 matching lines @@
     // The type is int32_t instead of HANDLE because HANDLE gets typedefed to
     // void*, whose size varies between 32 and 64-bit processes. Using a
     // int32_t means that 64-bit processes will need to perform both up-casting
     // and down-casting. This is performed using the appropriate Windows apis.
     int32_t handle;
     // The id of the destination process that the handle is duplicated into.
     base::ProcessId destination_process;
     AttachmentId attachment_id;
   };
 
-  HandleAttachmentWin(const HANDLE& handle);
+  explicit HandleAttachmentWin(const HANDLE& handle);
+  explicit HandleAttachmentWin(const WireFormat& wire_format);
 
   BrokerableType GetBrokerableType() const override;
 
   // Returns the wire format of this attachment.
   WireFormat GetWireFormat(const base::ProcessId& destination) const;
 
+  HANDLE get_handle() const { return handle_; }
+
  private:
   ~HandleAttachmentWin() override;
   HANDLE handle_;
 };
 
 }  // namespace internal
 }  // namespace IPC
 
 #endif  // IPC_HANDLE_ATTACHMENT_WIN_H_