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

chrome/browser/extensions/extension_apitest.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/extensions/extension_apitest.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/base_switches.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/browser/extensions/unpacked_installer.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/extensions/app_launch_params.h"
 #include "chrome/browser/ui/extensions/application_launch.h"
-#include "chrome/common/extensions/extension_process_policy.h"
 #include "chrome/test/base/ui_test_utils.h"
 #include "content/public/common/content_switches.h"
 #include "extensions/browser/api/test/test_api.h"
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/common/constants.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/extension_set.h"
 #include "extensions/common/switches.h"
 #include "extensions/test/result_catcher.h"
@@ skipping 413 matching lines @@
 }
 
 void ExtensionApiTest::SetUpCommandLine(base::CommandLine* command_line) {
   ExtensionBrowserTest::SetUpCommandLine(command_line);
   test_data_dir_ = test_data_dir_.AppendASCII("api_test");
   // Backgrounded renderer processes run at a lower priority, causing the
   // tests to take more time to complete. Disable backgrounding so that the
   // tests don't time out.
   command_line->AppendSwitch(switches::kDisableRendererBackgrounding);
 }