With --isolate-extensions, forking (via OpenURL) for extensions is not needed.

chrome/browser/browser_process_impl.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 "chrome/browser/browser_process_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <map>
@@ skipping 63 matching lines @@
 #include "chrome/browser/ui/browser_dialogs.h"
 #include "chrome/browser/ui/browser_finder.h"
 #include "chrome/browser/update_client/chrome_update_query_params_delegate.h"
 #include "chrome/common/channel_info.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/crash_keys.h"
 #include "chrome/common/extensions/chrome_extensions_client.h"
-#include "chrome/common/extensions/extension_process_policy.h"
 #include "chrome/common/features.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/switch_utils.h"
 #include "chrome/common/url_constants.h"
 #include "chrome/installer/util/google_update_settings.h"
 #include "components/component_updater/component_updater_service.h"
 #include "components/gcm_driver/gcm_driver.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/metrics/metrics_service.h"
 #include "components/metrics_services_manager/metrics_services_manager.h"
@@ skipping 1332 matching lines @@
 }
 
 void BrowserProcessImpl::OnAutoupdateTimer() {
   if (CanAutorestartForUpdate()) {
     DLOG(WARNING) << "Detected update.  Restarting browser.";
     RestartBackgroundInstance();
   }
 }
 
 #endif  // (defined(OS_WIN) || defined(OS_LINUX)) && !defined(OS_CHROMEOS)