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

apps/saved_files_service_factory.cc

Index: apps/saved_files_service_factory.cc
diff --git a/apps/saved_files_service_factory.cc b/apps/saved_files_service_factory.cc
index 4574209d1219b3d6106a4c4ccd966e5755a9b5d9..f85b315500c40f463a5743eb9a9acd76f76f8400 100644
--- a/apps/saved_files_service_factory.cc
+++ b/apps/saved_files_service_factory.cc
@@ -18,6 +18,13 @@ SavedFilesService* SavedFilesServiceFactory::GetForBrowserContext(
 }
 
 // static
+SavedFilesService* SavedFilesServiceFactory::GetForBrowserContextIfExists(
+    content::BrowserContext* context) {
+  return static_cast<SavedFilesService*>(
+      GetInstance()->GetServiceForBrowserContext(context, false));
+}
+
+// static
 SavedFilesServiceFactory* SavedFilesServiceFactory::GetInstance() {
   return base::Singleton<SavedFilesServiceFactory>::get();
 }