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

chrome/browser/platform_apps/platform_app_service_factory.h

 // Copyright (c) 2012 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_EXTENSIONS_PLATFORM_APP_SERVICE_FACTORY_H_
-#define CHROME_BROWSER_EXTENSIONS_PLATFORM_APP_SERVICE_FACTORY_H_
+#ifndef CHROME_BROWSER_PLATFORM_APPS_PLATFORM_APP_SERVICE_FACTORY_H_
+#define CHROME_BROWSER_PLATFORM_APPS_PLATFORM_APP_SERVICE_FACTORY_H_
 
 #include "base/memory/singleton.h"
-#include "chrome/browser/extensions/platform_app_service.h"
+#include "chrome/browser/platform_apps/platform_app_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/profiles/profile_keyed_service_factory.h"
 
-namespace extensions {
+namespace platform_apps {
 
 class PlatformAppServiceFactory : public ProfileKeyedServiceFactory {
  public:
   static PlatformAppService* GetForProfile(Profile* profile);
 
   static PlatformAppServiceFactory* GetInstance();
  private:
   friend struct DefaultSingletonTraits<PlatformAppServiceFactory>;
 
   PlatformAppServiceFactory();
   virtual ~PlatformAppServiceFactory();
 
   // ProfileKeyedServiceFactory
   virtual ProfileKeyedService* BuildServiceInstanceFor(
       Profile* profile) const OVERRIDE;
   virtual bool ServiceHasOwnInstanceInIncognito() const OVERRIDE;
   virtual bool ServiceIsCreatedWithProfile() const OVERRIDE;
   virtual bool ServiceIsNULLWhileTesting() const OVERRIDE;
 };
 
-}  // namespace extensions
+}  // namespace platform_apps
 
-#endif  // CHROME_BROWSER_EXTENSIONS_PLATFORM_APP_SERVICE_FACTORY_H_
+#endif  // CHROME_BROWSER_PLATFORM_APPS_PLATFORM_APP_SERVICE_FACTORY_H_