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

apps/saved_files_service_factory.cc

 // 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.
 
 #include "apps/saved_files_service_factory.h"
 
 #include "apps/saved_files_service.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "content/public/browser/browser_context.h"
 
 namespace apps {
 
 // static
 SavedFilesService* SavedFilesServiceFactory::GetForBrowserContext(
     content::BrowserContext* context) {
   return static_cast<SavedFilesService*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }
 
 // static
+SavedFilesService* SavedFilesServiceFactory::GetForBrowserContextIfExists(
+    content::BrowserContext* context) {
+  return static_cast<SavedFilesService*>(
+      GetInstance()->GetServiceForBrowserContext(context, false));
+}
+
+// static
 SavedFilesServiceFactory* SavedFilesServiceFactory::GetInstance() {
   return base::Singleton<SavedFilesServiceFactory>::get();
 }
 
 SavedFilesServiceFactory::SavedFilesServiceFactory()
     : BrowserContextKeyedServiceFactory(
           "SavedFilesService",
           BrowserContextDependencyManager::GetInstance()) {}
 
 SavedFilesServiceFactory::~SavedFilesServiceFactory() {}
 
 KeyedService* SavedFilesServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   return new SavedFilesService(context);
 }
 
 }  // namespace apps