Example of how to interpose yourself in a message stream.

chrome/renderer/chrome_content_renderer_client.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 "chrome/renderer/chrome_content_renderer_client.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/path_service.h"
 #include "base/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/common/child_process_logging.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
+#include "chrome/common/external_ipc_fuzzer.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_constants.h"
 #include "chrome/common/extensions/extension_set.h"
 #include "chrome/common/jstemplate_builder.h"
 #include "chrome/common/render_messages.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/renderer/autofill/autofill_agent.h"
 #include "chrome/renderer/autofill/form_manager.h"
 #include "chrome/renderer/autofill/password_autofill_manager.h"
 #include "chrome/renderer/automation/automation_renderer_helper.h"
@@ skipping 129 matching lines @@
   v8::Extension* search_extension = extensions_v8::SearchExtension::Get();
   // search_extension is null if not enabled.
   if (search_extension)
     thread->RegisterExtension(search_extension);
 
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDomAutomationController)) {
     thread->RegisterExtension(DomAutomationV8Extension::Get());
   }
 
+  if (CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableIPCFuzzing)) {
+    thread->channel()->set_outgoing_message_filter(LoadExternalIPCFuzzer());
+  }
   // chrome: pages should not be accessible by normal content, and should
   // also be unable to script anything but themselves (to help limit the damage
   // that a corrupt chrome: page could cause).
   WebString chrome_ui_scheme(ASCIIToUTF16(chrome::kChromeUIScheme));
   WebSecurityPolicy::registerURLSchemeAsDisplayIsolated(chrome_ui_scheme);
 
   // chrome-extension: resources shouldn't trigger insecure content warnings.
   WebString extension_scheme(ASCIIToUTF16(chrome::kExtensionScheme));
   WebSecurityPolicy::registerURLSchemeAsSecure(extension_scheme);
 }
@@ skipping 377 matching lines @@
   if (old_url.is_empty() && frame->opener())
     old_url = frame->opener()->url();
 
   bool old_url_is_hosted_app = extensions->GetByURL(old_url) &&
       !extensions->GetByURL(old_url)->web_extent().is_empty();
   return !extensions->InSameExtent(old_url, new_url) &&
          !old_url_is_hosted_app;
 }
 
 }  // namespace chrome