[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 <vector>
 
+#include "components/gcm_driver/common/gcm_messages.h"
+#include "components/gcm_driver/gcm_app_handler.h"
 #include "components/offline_pages/core/prefetch/prefetch_service.h"
 #include "url/gurl.h"
 
 namespace offline_pages {
 
-class PrefetchServiceImpl : public PrefetchService {
+class PrefetchServiceImpl : public PrefetchService, public gcm::GCMAppHandler {
  public:
   PrefetchServiceImpl();
   ~PrefetchServiceImpl() override;
 
+  std::string GetGCMAppId();
+
+  // GCMAppHandler implementation:
+  void ShutdownHandler() override;
+  void OnStoreReset() override;
+  void OnMessage(const std::string& app_id,
+                 const gcm::IncomingMessage& message) override;
+  void OnMessagesDeleted(const std::string& app_id) override;
+  void OnSendError(
+      const std::string& app_id,
+      const gcm::GCMClient::SendErrorDetails& send_error_details) override;
+  void OnSendAcknowledged(const std::string& app_id,
+                          const std::string& message_id) override;
+
   // PrefetchService 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;
 
   // KeyedService implementation:
   void Shutdown() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(PrefetchServiceImpl);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_CORE_PREFETCH_PREFETCH_SERVICE_IMPL_H_