[Offline Prefetch] Backoff support for PrefetchBackgroundTask

components/offline_pages/core/prefetch/prefetch_dispatcher_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_DISPATCHER_IMPL_H_
 #define COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_DISPATCHER_IMPL_H_
 
 #include "base/macros.h"
 #include "components/offline_pages/core/prefetch/prefetch_dispatcher.h"
 
 namespace offline_pages {
 
 class PrefetchDispatcherImpl : public PrefetchDispatcher {
  public:
   PrefetchDispatcherImpl();
   ~PrefetchDispatcherImpl() override;
 
   // PrefetchDispatcher implementation:
   void AddCandidatePrefetchURLs(
       const std::vector<PrefetchURL>& suggested_urls) override;
   void RemoveAllUnprocessedPrefetchURLs(const std::string& name_space) override;
   void RemovePrefetchURLsByClientId(const ClientId& client_id) override;
   void BeginBackgroundTask(std::unique_ptr<ScopedBackgroundTask> task) override;
-  void StopBackgroundTask(ScopedBackgroundTask* task) override;
+  void StopBackgroundTask() override;
+  void RequestFinishBackgroundTaskForTest() override;
 
  private:
+  void DisposeTask();
+
+  std::unique_ptr<ScopedBackgroundTask> task_;
+
   DISALLOW_COPY_AND_ASSIGN(PrefetchDispatcherImpl);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_DISPATCHER_IMPL_H_