[Offline Pages] Two-step expiration in storage manager.

components/offline_pages/offline_page_model.h

Index: components/offline_pages/offline_page_model.h
diff --git a/components/offline_pages/offline_page_model.h b/components/offline_pages/offline_page_model.h
index 0e336ccf4144bdf21a1cb799879efa31d07dbb7f..03aba53e238e2e1a87e6c0166cca27c268e70f04 100644
--- a/components/offline_pages/offline_page_model.h
+++ b/components/offline_pages/offline_page_model.h
@@ -218,7 +218,8 @@ class OfflinePageModel : public KeyedService,
   // Marks pages as expired and removes their respective files from the archive
   // directory.
   void ExpirePages(const std::vector<int64_t>& offline_ids,
-                   const base::Time& expiration_time);
+                   const base::Time& expiration_time,
+                   const base::Callback<void(bool)>& callback) override;
 
   // Returns the policy controller.
   ClientPolicyController* GetPolicyController();