Example of how to interpose yourself in a message stream.

content/common/child_thread.cc

 // Copyright (c) 2011 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 "content/common/child_thread.h"
 
 #include "base/message_loop.h"
 #include "base/string_util.h"
 #include "base/command_line.h"
 #include "content/common/child_process.h"
@@ skipping 109 matching lines @@
 
   router_.RemoveRoute(routing_id);
 }
 
 IPC::Channel::Listener* ChildThread::ResolveRoute(int32 routing_id) {
   DCHECK(MessageLoop::current() == message_loop());
 
   return router_.ResolveRoute(routing_id);
 }
 
+void ChildThread::SetOutgoingMessageFilter(IPC::OutgoingMessageFilter* filter){
+  channel_->set_outgoing_message_filter(filter);
+}
+
 webkit_glue::ResourceLoaderBridge* ChildThread::CreateBridge(
     const webkit_glue::ResourceLoaderBridge::RequestInfo& request_info) {
   return resource_dispatcher()->CreateBridge(request_info);
 }
 
 ResourceDispatcher* ChildThread::resource_dispatcher() {
   return resource_dispatcher_.get();
 }
 
 IPC::SyncMessageFilter* ChildThread::sync_message_filter() {
@@ skipping 65 matching lines @@
     MessageLoop::current()->Quit();
     return;
   }
 
   // The child process shutdown sequence is a request response based mechanism,
   // where we send out an initial feeler request to the child process host
   // instance in the browser to verify if it's ok to shutdown the child process.
   // The browser then sends back a response if it's ok to shutdown.
   Send(new ChildProcessHostMsg_ShutdownRequest);
 }