IPC: Fix attachment brokering race condition.

ipc/ipc_channel_proxy.cc

 // Copyright (c) 2012 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/ipc_channel_proxy.h"
 
 #include <stddef.h>
 #include <stdint.h>
 #include <utility>
 
@@ skipping 468 matching lines @@
   DCHECK(CalledOnValidThread());
 
   context()->ClearIPCTaskRunner();
 }
 
 base::ProcessId ChannelProxy::GetPeerPID() const {
   return context_->peer_pid_;
 }
 
 void ChannelProxy::OnSetAttachmentBrokerEndpoint() {
+  CHECK(!did_init_);
   context()->set_attachment_broker_endpoint(is_attachment_broker_endpoint());
 }
 
 #if defined(OS_POSIX) && !defined(OS_NACL_SFI)
 // See the TODO regarding lazy initialization of the channel in
 // ChannelProxy::Init().
 int ChannelProxy::GetClientFileDescriptor() {
   DCHECK(CalledOnValidThread());
 
   Channel* channel = context_.get()->channel_.get();
@@ skipping 11 matching lines @@
   return channel->TakeClientFileDescriptor();
 }
 #endif
 
 void ChannelProxy::OnChannelInit() {
 }
 
 //-----------------------------------------------------------------------------
 
 }  // namespace IPC