[Offline Pages] Remove activation time for background loading.

components/offline_pages/core/background/request_queue_store_sql.h

Index: components/offline_pages/core/background/request_queue_store_sql.h
diff --git a/components/offline_pages/core/background/request_queue_store_sql.h b/components/offline_pages/core/background/request_queue_store_sql.h
index 6bd9b9a4ccdd79d54592fb3a012f4704b7d587dd..7c694f39db754dff923edb247e31935a83241030 100644
--- a/components/offline_pages/core/background/request_queue_store_sql.h
+++ b/components/offline_pages/core/background/request_queue_store_sql.h
@@ -24,6 +24,17 @@ class Connection;
 namespace offline_pages {
 
 // SQLite implementation of RequestQueueStore.
+//
+// This store has a history of schema updates.
+// Original schema was delivered in M57. Since then the following changes
+// happened:
+// * In M58 original_url was added.
+//
+// TODO(romax): remove all activation_time related code the next we change the
+// schema.
+//
+// Looking for procesure to update the schema, please refer to
+// offline_page_metadata_store_sql.h
 class RequestQueueStoreSQL : public RequestQueueStore {
  public:
   RequestQueueStoreSQL(