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

apps/browser_context_keyed_service_factories.h

Index: apps/browser_context_keyed_service_factories.h
diff --git a/apps/browser_context_keyed_service_factories.h b/apps/browser_context_keyed_service_factories.h
index 2e206d595eb5ee81d13a25e8b839b9ebe82f7d31..45b9c2f23626415d971be960d8f232514f78a044 100644
--- a/apps/browser_context_keyed_service_factories.h
+++ b/apps/browser_context_keyed_service_factories.h
@@ -5,12 +5,20 @@
 #ifndef APPS_BROWSER_CONTEXT_KEYED_SERVICE_FACTORIES_H_
 #define APPS_BROWSER_CONTEXT_KEYED_SERVICE_FACTORIES_H_
 
+namespace content {
+class BrowserContext;
+}
+
 namespace apps {
 
 // Ensures the existence of any BrowserContextKeyedServiceFactory provided by
 // the core apps code.
 void EnsureBrowserContextKeyedServiceFactoriesBuilt();
 
+// Notifies the relevant BrowserContextKeyedServices for the browser context
+// that the application is being terminated.
+void NotifyApplicationTerminating(content::BrowserContext* browser_context);
+
 }  // namespace apps
 
 #endif  // APPS_BROWSER_CONTEXT_KEYED_SERVICE_FACTORIES_H_