Enable the mojo-based serial API in the renderer behind a flag.

extensions/test/test_service_registration_manager.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 "extensions/test/test_service_registration_manager.h"
+
+namespace extensions {
+
+TestServiceRegistrationManager::TestServiceRegistrationManager() {
+  ServiceRegistrationManager::SetServiceRegistrationManagerForTest(this);
+}
+
+TestServiceRegistrationManager::~TestServiceRegistrationManager() {
+  ServiceRegistrationManager::SetServiceRegistrationManagerForTest(nullptr);
+}
+
+void TestServiceRegistrationManager::AddServiceToServiceRegistry(
+    content::ServiceRegistry* service_registry,
+    internal::ServiceFactoryBase* factory) {
+  auto test_factory = test_factories_.find(factory->GetName());
+  if (test_factory != test_factories_.end()) {
+    test_factory->second->Register(service_registry);
+  } else {
+    ServiceRegistrationManager::AddServiceToServiceRegistry(service_registry,
+                                                            factory);
+  }
+}
+
+}  // namespace extensions