Reland #1: Clean up interface of attachment broker.

ipc/attachment_broker_privileged.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_privileged.h"
 
 #include <algorithm>
 
 #include "ipc/ipc_channel.h"
 
 namespace IPC {
 
 AttachmentBrokerPrivileged::AttachmentBrokerPrivileged() {}
 
 AttachmentBrokerPrivileged::~AttachmentBrokerPrivileged() {}
 
 void AttachmentBrokerPrivileged::RegisterCommunicationChannel(
     Channel* channel) {
+  channel->set_attachment_broker_endpoint(true);
   auto it = std::find(channels_.begin(), channels_.end(), channel);
   DCHECK(channels_.end() == it);
   channels_.push_back(channel);
 }
 
 void AttachmentBrokerPrivileged::DeregisterCommunicationChannel(
     Channel* channel) {
   auto it = std::find(channels_.begin(), channels_.end(), channel);
   if (it != channels_.end())
     channels_.erase(it);
 }
 
 Channel* AttachmentBrokerPrivileged::GetChannelWithProcessId(
     base::ProcessId id) {
   auto it = std::find_if(channels_.begin(), channels_.end(),
                          [id](Channel* c) { return c->GetPeerPID() == id; });
   if (it == channels_.end())
     return nullptr;
   return *it;
 }
 
 }  // namespace IPC