ipc: Change the timing of the construction of the attachment broker.

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>
 
 namespace {
 IPC::AttachmentBroker* g_attachment_broker = nullptr;
 }
 
 namespace IPC {
 
 // static
 void AttachmentBroker::SetGlobal(AttachmentBroker* broker) {
-  // TODO(erikchen): There should be a CHECK here to make sure that
-  // |g_attachment_broker| is nullptr. Right now, this causes problems with
-  // --single_process and similar testing conditions. I'm temporarily removing
-  // this CHECK. http://crbug.com/534539.
+  CHECK(!g_attachment_broker);
   g_attachment_broker = broker;
 }
 
 // static
 AttachmentBroker* AttachmentBroker::GetGlobal() {
   return g_attachment_broker;
 }
 
 AttachmentBroker::AttachmentBroker() {}
 AttachmentBroker::~AttachmentBroker() {}
@@ skipping 33 matching lines @@
 void AttachmentBroker::NotifyObservers(
     const BrokerableAttachment::AttachmentId& id) {
   // Make a copy of observers_ to avoid mutations during iteration.
   std::vector<Observer*> observers = observers_;
   for (Observer* observer : observers) {
     observer->ReceivedBrokerableAttachmentWithId(id);
   }
 }
 
 }  // namespace IPC