Eliminate a potential race in IPC::ChannelProxy

ipc/ipc_channel_proxy.h

 // 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.
 
 #ifndef IPC_IPC_CHANNEL_PROXY_H_
 #define IPC_IPC_CHANNEL_PROXY_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 215 matching lines @@
     void AddFilter(MessageFilter* filter);
     void OnDispatchConnected();
     void OnDispatchError();
 
     scoped_refptr<base::SingleThreadTaskRunner> listener_task_runner_;
     Listener* listener_;
 
     // List of filters.  This is only accessed on the IPC thread.
     std::vector<scoped_refptr<MessageFilter> > filters_;
     scoped_refptr<base::SingleThreadTaskRunner> ipc_task_runner_;
+
+    // Note, channel_ may be set on the Listener thread or the IPC thread.
+    // But once it has been set, it must only be read or cleared on the IPC
+    // thread.
     scoped_ptr<Channel> channel_;
     std::string channel_id_;
     bool channel_connected_called_;
 
     // Routes a given message to a proper subset of |filters_|, depending
     // on which message classes a filter might support.
     class MessageFilterRouter;
     scoped_ptr<MessageFilterRouter> message_filter_router_;
 
     // Holds filters between the AddFilter call on the listerner thread and the
@@ skipping 17 matching lines @@
   // that involves this data.
   scoped_refptr<Context> context_;
 
   // Whether the channel has been initialized.
   bool did_init_;
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_PROXY_H_