Favorites table is copied as a separate table name during the first grid migration.
On subsequent migrations this backup table is used if it exists, otherwise new
backup is created. The backup table is also removed if there is any insert or
delete operation on the db (outside of the migration operation itself).
Bug: 111850268
Bug: 121048571
Change-Id: I6f02f4a355c369ee99d89430971be258f7516f6e
Sunny Goyal