Add chrome/browser/apps/BUILD.gn and move Chrome-specific code there

apps/app_load_service_factory.h

-// Copyright 2013 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.
-
-#ifndef APPS_APP_LOAD_SERVICE_FACTORY_H_
-#define APPS_APP_LOAD_SERVICE_FACTORY_H_
-
-#include "base/memory/singleton.h"
-#include "components/keyed_service/content/browser_context_keyed_service_factory.h"
-
-namespace content {
-class BrowserContext;
-}
-
-namespace apps {
-
-class AppLoadService;
-
-class AppLoadServiceFactory : public BrowserContextKeyedServiceFactory {
- public:
-  static AppLoadService* GetForBrowserContext(content::BrowserContext* context);
-
-  static AppLoadServiceFactory* GetInstance();
-
- private:
-  friend struct base::DefaultSingletonTraits<AppLoadServiceFactory>;
-
-  AppLoadServiceFactory();
-  ~AppLoadServiceFactory() override;
-
-  // BrowserContextKeyedServiceFactory:
-  KeyedService* BuildServiceInstanceFor(
-      content::BrowserContext* context) const override;
-  bool ServiceIsCreatedWithBrowserContext() const override;
-  bool ServiceIsNULLWhileTesting() const override;
-  content::BrowserContext* GetBrowserContextToUse(
-      content::BrowserContext* context) const override;
-};
-
-}  // namespace apps
-
-#endif  // APPS_APP_LOAD_SERVICE_FACTORY_H_