Summary: The new table factory is used if users want to convert a DB from one table format to the other. A user can use this table to open a DB written using one table format and write new files to another table format.
Test Plan: add a unit test
Reviewers: haobo, igor
Reviewed By: igor
Subscribers: dhruba, ljin, yhchiang, leveldb
Differential Revision: https://reviews.facebook.net/D19017
