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

chrome/browser/apps/browser_context_keyed_service_factories.h

+// Copyright 2017 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 CHROME_BROWSER_APPS_BROWSER_CONTEXT_KEYED_SERVICE_FACTORIES_H_
+#define CHROME_BROWSER_APPS_BROWSER_CONTEXT_KEYED_SERVICE_FACTORIES_H_
+
+namespace content {
+class BrowserContext;
+}
+
+namespace chrome_apps {
+
+// Ensures the existence of any BrowserContextKeyedServiceFactory provided by
+// the Chrome 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 chrome_apps
+
+#endif  // CHROME_BROWSER_APPS_BROWSER_CONTEXT_KEYED_SERVICE_FACTORIES_H_