With the revert of Hera, see http://crbug.com/582539 and http://crbug.com/597147, this code is no longer used. It adds to the maintenance overhead of tab models and complicates reasoning about TabPersistentStore and other classes whose methods were used only in migration (outside of their own classes).
This code should be removed.
Comment 1 by wnwen@chromium.org
, May 16 2016