[Offline Pages] Add expiration in internal log.

components/offline_pages/offline_page_model_event_logger.h

 // Copyright 2016 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_OFFLINE_PAGE_MODEL_EVENT_LOGGER_H_
 #define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_EVENT_LOGGER_H_
 
 #include "components/offline_pages/offline_event_logger.h"
 
 namespace offline_pages {
 
 class OfflinePageModelEventLogger : public OfflineEventLogger {
  public:
   // Records that a page has been saved for |name_space| with |url|
   // and |offline_id|.
   void RecordPageSaved(const std::string& name_space,
                        const std::string& url,
                        const std::string& offline_id);
 
   // Records that a page with |offline_id| has been deleted.
   void RecordPageDeleted(const std::string& offline_id);
 
+  // Records that a page with |offline_id| has been expired.
+  void RecordPageExpired(const std::string& offline_id);
+
   // Records that the offline store has been cleared.
   void RecordStoreCleared();
 
   // Records that there was an error when clearing the offline store.
   void RecordStoreClearError();
 
   // Records that there was an error when reloading the offline store.
   void RecordStoreReloadError();
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_MODEL_EVENT_LOGGER_H_