Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_service_impl.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_IMPL_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "components/offline_pages/core/prefetch/prefetch_service.h"
 
 namespace offline_pages {
+class PrefetchStore;
 
 class PrefetchServiceImpl : public PrefetchService {
  public:
-  PrefetchServiceImpl();
+  PrefetchServiceImpl(std::unique_ptr<PrefetchStore> store);
   ~PrefetchServiceImpl() override;
 
   // PrefetchService implementation:
   PrefetchDispatcher* GetDispatcher() override;
 
   // KeyedService implementation:
   void Shutdown() override;
 
  private:
   std::unique_ptr<PrefetchDispatcher> dispatcher_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefetchServiceImpl);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_