Add title update merge logic to reading list entry

components/reading_list/ios/reading_list_store.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_READING_LIST_IOS_READING_LIST_STORE_H_
 #define COMPONENTS_READING_LIST_IOS_READING_LIST_STORE_H_
 
 #include "base/threading/non_thread_safe.h"
 #include "components/reading_list/ios/reading_list_model_storage.h"
 #include "components/reading_list/ios/reading_list_store_delegate.h"
@@ skipping 55 matching lines @@
   syncer::SyncError ApplySyncChanges(
       std::unique_ptr<syncer::MetadataChangeList> metadata_change_list,
       syncer::EntityChangeList entity_changes) override;
 
   // Returns whether entries respect a strict order for sync and if |rhs| can be
   // submitted to sync after |lhs| has been received.
   // The order should ensure that there is no sync loop in sync and should be
   // submitted to sync in strictly increasing order.
   // Entries are in increasing order if all the fields respect increasing order.
   // - URL must be the same.
-  // - title must verify rhs.title.compare(lhs.title) >= 0
+  // - update_title_time_us:
+  //       rhs.update_title_time_us >= lhs.update_title_time_us
+  // - title:
+  //       if rhs.update_title_time_us > lhs.update_title_time_us
+  //         title can be anything
+  //       if rhs.update_title_time_us == lhs.update_title_time_us
+  //         title must verify rhs.title.compare(lhs.title) >= 0
   // - creation_time_us:
   //       rhs.creation_time_us >= lhs.creation_time_us
   // - rhs.first_read_time_us:
   //       if rhs.creation_time_us > lhs.creation_time_us,
   //         rhs.first_read_time_us can be anything.
   //       if rhs.creation_time_us == lhs.creation_time_us
   //           and rhs.first_read_time_us == 0
   //         rhs.first_read_time_us can be anything.
   //       if rhs.creation_time_us == lhs.creation_time_us,
   //         rhs.first_read_time_us <= lhs.first_read_time_us
@@ skipping 63 matching lines @@
   std::unique_ptr<syncer::ModelTypeStore> store_;
   ReadingListModel* model_;
   ReadingListStoreDelegate* delegate_;
   StoreFactoryFunction create_store_callback_;
 
   int pending_transaction_count_;
   std::unique_ptr<syncer::ModelTypeStore::WriteBatch> batch_;
 };
 
 #endif  // COMPONENTS_READING_LIST_IOS_READING_LIST_STORE_H_