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

components/offline_pages/core/prefetch/prefetch_service_impl.h

Index: components/offline_pages/core/prefetch/prefetch_service_impl.h
diff --git a/components/offline_pages/core/prefetch/prefetch_service_impl.h b/components/offline_pages/core/prefetch/prefetch_service_impl.h
index 69346aa356ad721f13d34b818cdb714cced3531d..8f6fbbd51263457054368eb7c792db30ebcabfbf 100644
--- a/components/offline_pages/core/prefetch/prefetch_service_impl.h
+++ b/components/offline_pages/core/prefetch/prefetch_service_impl.h
@@ -7,16 +7,32 @@
 
 #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;