[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/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