Create a new chrome/browser/apps folder and move PlatformAppService there.

chrome/browser/platform_apps/platform_app_service.h

Index: chrome/browser/platform_apps/platform_app_service.h
diff --git a/chrome/browser/extensions/platform_app_service.h b/chrome/browser/platform_apps/platform_app_service.h
similarity index 81%
rename from chrome/browser/extensions/platform_app_service.h
rename to chrome/browser/platform_apps/platform_app_service.h
index 28a578dcc8686a69a4d1691acfc2a3b396365a46..9379ec907e73f91c98ab388caed8ca13f0b0caf3 100644
--- a/chrome/browser/extensions/platform_app_service.h
+++ b/chrome/browser/platform_apps/platform_app_service.h
@@ -2,15 +2,15 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef CHROME_BROWSER_EXTENSIONS_PLATFORM_APP_SERVICE_H_
-#define CHROME_BROWSER_EXTENSIONS_PLATFORM_APP_SERVICE_H_
+#ifndef CHROME_BROWSER_PLATFORM_APPS_PLATFORM_APP_SERVICE_H_
+#define CHROME_BROWSER_PLATFORM_APPS_PLATFORM_APP_SERVICE_H_
 
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_keyed_service.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
-namespace extensions {
+namespace platform_apps {
 
 // The PlatformAppService provides services for platform apps, such as
 // keeping the browser process alive while they are running.
@@ -30,6 +30,6 @@ class PlatformAppService : public ProfileKeyedService,
   content::NotificationRegistrar registrar_;
 };
 
-}  // namespace extensions
+}  // namespace platform_apps
 
-#endif  // CHROME_BROWSER_EXTENSIONS_PLATFORM_APP_SERVICE_H_
+#endif  // CHROME_BROWSER_PLATFORM_APPS_PLATFORM_APP_SERVICE_H_