The saveAndUpdateEntries() method was always saving entries under the current entity's revisionKey, and then always deleting them under the old entity's revisionKey - even if the revisionKeys were the same (i.e., we didn't change any entry content in the list, in which case the builder's build() method doesn't create a new revisionKey).
This would have caused the existing entries to be unnecessarily resaved, and (worse) then caused those same existing entries to all be deleted.
This fixes the bug by only resaving entries when the revisionKey has changed.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=124873871
6466ad51f6