Extend CHECKSUM TABLE to checksum only parts (chunks) of the table

Extend CHECKSUM TABLE so that it's possible to checksum only parts (chunks) of the table, or the whole table in chunks.

Clearly the intent is to have built-in pt-table-checksum so same restrictions apply (table must have PK/UNIQUE) and likely we would love to see some parameters from it too: chunk-size, chunk-time, max-load, function, columns?, float-precision?

Also this implies the statement will be replicated and that it would require a table for storing results like --replicate (stored in mysql schema?)

One addition would be the capacity to use WHERE so one could checksum custom sets of data instead of PK/UNIQUE ranges.

Maybe it should be a plugin instead of an extension to CHECKSUM TABLE?