[Offline Pages] Removes two-step expiration related.

components/offline_pages/offline_page_metadata_store_sql.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_METADATA_STORE_SQL_H_
 #define COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_METADATA_STORE_SQL_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 17 matching lines @@
 // which is implemented using a SQLite database.
 //
 // This store has a history of schema updates in pretty much every release.
 // Original schema was delivered in M52. Since then, the following changes
 // happened:
 // * In M53 expiration_time was added,
 // * In M54 title was added,
 // * In M55 we dropped the following fields (never used): version, status,
 //   offline_url, user_initiated.
 // * In M56 original_url was added.
+// * In M57 expiration_time was dropped. Existing expired pages would be
+//   removed when metadata consistency check happens.
 //
 // Here is a procedure to update the schema for this store:
 // * Decide how to detect that the store is on a particular version, which
 //   typically means that a certain field exists or is missing. This happens in
 //   Upgrade section of |CreateSchema|
 // * Work out appropriate change and apply it to all existing upgrade paths. In
 //   the interest of performing a single update of the store, it upgrades from a
 //   detected version to the current one. This means that when making a change,
 //   more than a single query may have to be updated (in case of fields being
 //   removed or needed to be initialized to a specific, non-default value).
@@ skipping 46 matching lines @@
   StoreState state_;
 
   base::WeakPtrFactory<OfflinePageMetadataStoreSQL> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(OfflinePageMetadataStoreSQL);
 };
 
 }  // namespace offline_pages
 
 #endif  // COMPONENTS_OFFLINE_PAGES_OFFLINE_PAGE_METADATA_STORE_SQL_H_