Create skeleton for the Prefetching store and initial pipeline step.

components/offline_pages/core/prefetch/prefetch_service_impl.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/core/prefetch/prefetch_service_impl.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "components/offline_pages/core/prefetch/prefetch_dispatcher_impl.h"
 
 namespace offline_pages {
 
-PrefetchServiceImpl::PrefetchServiceImpl()
-    : dispatcher_(base::MakeUnique<PrefetchDispatcherImpl>()) {}
+PrefetchServiceImpl::PrefetchServiceImpl(std::unique_ptr<PrefetchStore> store)
+    : dispatcher_(base::MakeUnique<PrefetchDispatcherImpl>(std::move(store))) {}
 
 PrefetchServiceImpl::~PrefetchServiceImpl() = default;
 
 PrefetchDispatcher* PrefetchServiceImpl::GetDispatcher() {
   return dispatcher_.get();
 };
 
 void PrefetchServiceImpl::Shutdown() {}
 
 }  // namespace offline_pages