[Offline Pages] Add a GCMAppHandler for offline page prefetch.

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_gcm_handler.h"
 #include "components/offline_pages/core/prefetch/prefetch_service.h"
+#include "components/offline_pages/core/prefetch/suggested_articles_observer.h"
+
+namespace ntp_snippets {
+class ContentSuggestionsService;
+}
 
 namespace offline_pages {
 
 class PrefetchServiceImpl : public PrefetchService {
  public:
   PrefetchServiceImpl();
   ~PrefetchServiceImpl() override;
 
   // PrefetchService implementation:
+  void ObserveContentSuggestionsService(
+      ntp_snippets::ContentSuggestionsService* service) override;
+  void AddPrefetchGCMHandler(
+      std::unique_ptr<PrefetchGCMHandler> app_handler) override;
   PrefetchDispatcher* GetDispatcher() override;
 
   // KeyedService implementation:
   void Shutdown() override;
 
  private:
+  std::unique_ptr<SuggestedArticlesObserver> suggested_articles_observer_;
+  std::unique_ptr<PrefetchGCMHandler> gcm_handler_;
+
   std::unique_ptr<PrefetchDispatcher> dispatcher_;
-
   DISALLOW_COPY_AND_ASSIGN(PrefetchServiceImpl);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_