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

chrome/browser/apps/app_load_service.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_H_
-#define APPS_APP_LOAD_SERVICE_H_
+#ifndef CHROME_BROWSER_APPS_APP_LOAD_SERVICE_H_
+#define CHROME_BROWSER_APPS_APP_LOAD_SERVICE_H_
 
 #include <map>
 #include <string>
 
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "components/keyed_service/core/keyed_service.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "extensions/browser/extension_registry_observer.h"
@@ skipping 76 matching lines @@
   // no action.
   std::map<std::string, PostReloadAction> post_reload_actions_;
   content::NotificationRegistrar registrar_;
   content::BrowserContext* context_;
 
   DISALLOW_COPY_AND_ASSIGN(AppLoadService);
 };
 
 }  // namespace apps
 
-#endif  // APPS_APP_LOAD_SERVICE_H_
+#endif  // CHROME_BROWSER_APPS_APP_LOAD_SERVICE_H_