Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_service.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 COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_
 
 #include "components/keyed_service/core/keyed_service.h"
 
 namespace ntp_snippets {
 class ContentSuggestionsService;
 }
 
 namespace offline_pages {
-
 class OfflineMetricsCollector;
 class PrefetchDispatcher;
 class PrefetchGCMHandler;
+class PrefetchStore;
 
 // Main class and entry point for the Offline Pages Prefetching feature, that
 // controls the lifetime of all major subcomponents of the prefetching system.
 class PrefetchService : public KeyedService {
  public:
   ~PrefetchService() override = default;
 
   // Subobjects that are created and owned by this service. Creation should be
   // lightweight, all heavy work must be done on-demand only.
   // The service manages lifetime, hookup and initialization of Prefetch
   // system that consists of multiple specialized objects, all vended by this
   // service. All pointers are raw and are always valid.
-  virtual PrefetchDispatcher* GetDispatcher() = 0;
   virtual OfflineMetricsCollector* GetOfflineMetricsCollector() = 0;
+  virtual PrefetchDispatcher* GetPrefetchDispatcher() = 0;
   virtual PrefetchGCMHandler* GetPrefetchGCMHandler() = 0;
+  virtual PrefetchStore* GetPrefetchStore() = 0;
 
   // Called at construction of the ContentSuggestionsService to begin observing
   // events related to incoming articles.
   virtual void ObserveContentSuggestionsService(
       ntp_snippets::ContentSuggestionsService* service) = 0;
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_H_