Add support for Attachment Brokering of IPC::Channels on multiple threads.

ipc/attachment_broker.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/attachment_broker.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 63 matching lines @@
 void AttachmentBroker::RemoveObserver(AttachmentBroker::Observer* observer) {
   base::AutoLock auto_lock(*get_lock());
   auto it = std::find_if(observers_.begin(), observers_.end(),
                       [observer](const ObserverInfo& info) {
                         return info.observer == observer;
                       });
   if (it != observers_.end())
     observers_.erase(it);
 }
 
-void AttachmentBroker::RegisterCommunicationChannel(Endpoint* endpoint) {
+void AttachmentBroker::RegisterCommunicationChannel(
+    Endpoint* endpoint,
+    scoped_refptr<base::SingleThreadTaskRunner> runner) {
   NOTREACHED();
 }
 
 void AttachmentBroker::DeregisterCommunicationChannel(Endpoint* endpoint) {
   NOTREACHED();
 }
 
 void AttachmentBroker::RegisterBrokerCommunicationChannel(Endpoint* endpoint) {
   NOTREACHED();
 }
@@ skipping 51 matching lines @@
 
   observer->ReceivedBrokerableAttachmentWithId(id);
 }
 
 AttachmentBroker::ObserverInfo::ObserverInfo() {}
 AttachmentBroker::ObserverInfo::ObserverInfo(const ObserverInfo& other) =
     default;
 AttachmentBroker::ObserverInfo::~ObserverInfo() {}
 
 }  // namespace IPC