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

chrome/browser/extensions/chrome_extension_web_contents_observer.cc

 // Copyright 2014 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/extensions/chrome_extension_web_contents_observer.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/extensions/error_console/error_console.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/window_controller.h"
 #include "chrome/browser/metrics/chrome_metrics_service_accessor.h"
 #include "chrome/common/extensions/chrome_extension_messages.h"
-#include "chrome/common/extensions/extension_process_policy.h"
 #include "chrome/common/url_constants.h"
 #include "components/rappor/rappor_service_impl.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/child_process_security_policy.h"
 #include "content/public/browser/navigation_handle.h"
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/common/content_switches.h"
 #include "extensions/browser/extension_registry.h"
@@ skipping 120 matching lines @@
   // TODO(yoz): This reload doesn't happen synchronously for unpacked
   //            extensions. It seems to be fast enough, but there is a race.
   //            We should delay loading until the extension has reloaded.
   if (registry->GetExtensionById(extension_id, ExtensionRegistry::TERMINATED)) {
     ExtensionSystem::Get(browser_context())->
         extension_service()->ReloadExtension(extension_id);
   }
 }
 
 }  // namespace extensions