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

apps/browser_context_keyed_service_factories.h

 // Copyright 2014 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_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_