Create a strict order in ReadingListSpecifics

components/reading_list/ios/reading_list_store.h

Index: components/reading_list/ios/reading_list_store.h
diff --git a/components/reading_list/ios/reading_list_store.h b/components/reading_list/ios/reading_list_store.h
index ab90ca43d584cee4962e813e9dbc97d72adf9a81..4dd3cfe88bc71469738958370b52dfa4afb5b842 100644
--- a/components/reading_list/ios/reading_list_store.h
+++ b/components/reading_list/ios/reading_list_store.h
@@ -72,6 +72,21 @@ class ReadingListStore : public syncer::ModelTypeSyncBridge,
       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

[pavely, 2016/12/07 19:16:06]

I don't really understand why title is taken into account for comparison. What
if in the future chrome allows to rename articles and user shortens title? Will
it be rejected by other clients?

[Olivier, 2016/12/08 08:04:07]

At the moment, title cannot be changed, so the only conflict can appear if one
device does have a title and the other does not.
If we add the possibility to change the title, we will need to set a new field
like "last_title_change_timestamp" to handle conflicts.

+  // - rhs.creation_time_us >= lhs.creation_time_us
+  // - rhs.update_time_us >= lhs.update_time_us
+  // - if rhs.update_time_us > lhs.update_time_us, rhs.state can be anything.
+  // - if rhs.update_time_us == lhs.update_time_us, rhs.state >= lhs.state in
+  //          the order UNSEEN, UNREAD, READ.
+  static bool CompareEntriesForSync(const sync_pb::ReadingListSpecifics& lhs,
+                                    const sync_pb::ReadingListSpecifics& rhs);
+
   // Asynchronously retrieve the corresponding sync data for |storage_keys|.
   void GetData(StorageKeyList storage_keys, DataCallback callback) override;