[Offline Pages] Add a GCMAppHandler for offline page prefetch.

components/offline_pages/content/prefetch_service_factory.cc

 // 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.
 
 #include "components/offline_pages/content/prefetch_service_factory.h"
 
 #include "base/memory/singleton.h"
+#include "components/gcm_driver/gcm_driver.h"
+#include "components/gcm_driver/gcm_profile_service.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "components/offline_pages/core/prefetch/prefetch_service_impl.h"
 #include "content/public/browser/browser_context.h"
 
 namespace offline_pages {
 
 PrefetchServiceFactory::PrefetchServiceFactory()
     : BrowserContextKeyedServiceFactory(
           "OfflinePagePrefetchService",
           BrowserContextDependencyManager::GetInstance()) {}
 
 // static
 PrefetchServiceFactory* PrefetchServiceFactory::GetInstance() {
   return base::Singleton<PrefetchServiceFactory>::get();
 }
 
 // static
 PrefetchService* PrefetchServiceFactory::GetForBrowserContext(
     content::BrowserContext* context) {
   return static_cast<PrefetchService*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }
 
 KeyedService* PrefetchServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* context) const {
   return new PrefetchServiceImpl();
 }
 
 }  // namespace offline_pages