Make attachment broker a subclass of IPC::Listener.

ipc/brokerable_attachment.cc

 // 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.
 
 #include "ipc/brokerable_attachment.h"
 
 #include "crypto/random.h"
 
 namespace IPC {
 
 namespace {
 
 BrokerableAttachment::AttachmentId GetRandomId() {
   BrokerableAttachment::AttachmentId id;
   crypto::RandBytes(id.nonce, BrokerableAttachment::kNonceSize);
   return id;
 }
 
 }  // namespace
 
 BrokerableAttachment::BrokerableAttachment() : id_(GetRandomId()) {
 }
 
+BrokerableAttachment::BrokerableAttachment(const AttachmentId& id) : id_(id) {
+}
+
 BrokerableAttachment::~BrokerableAttachment() {
 }
 
 BrokerableAttachment::AttachmentId BrokerableAttachment::GetIdentifier() const {
   return id_;
 }
 
 BrokerableAttachment::Type BrokerableAttachment::GetType() const {
   return TYPE_BROKERABLE_ATTACHMENT;
 }
 
 }  // namespace IPC