ipc: Add a lock to guard modifications of state of the AttachmentBroker.

ipc/attachment_broker_privileged_mac.h

 // 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.
 
 #ifndef IPC_ATTACHMENT_BROKER_PRIVILEGED_MAC_H_
 #define IPC_ATTACHMENT_BROKER_PRIVILEGED_MAC_H_
 
 #include <mach/mach.h>
 
 #include "base/gtest_prod_util.h"
@@ skipping 105 matching lines @@
   // Makes an attachment, queues it, and notifies the observers.
   void RouteWireFormatToSelf(const MachPortWireFormat& wire_format);
 
   // |wire_format.destination_process| must be another process.
   // |wire_format.mach_port| must be the intermediate Mach port.
   // Ownership of |wire_format.mach_port| is implicitly passed to the process
   // that receives the Chrome IPC message.
   void RouteWireFormatToAnother(const MachPortWireFormat& wire_format);
 
   // The port provider must live at least as long as the AttachmentBroker.
-  base::PortProvider* port_provider_;
+  const base::PortProvider* port_provider_;
 
   DISALLOW_COPY_AND_ASSIGN(AttachmentBrokerPrivilegedMac);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_ATTACHMENT_BROKER_PRIVILEGED_MAC_H_