Summary:
we were passing `record_read_stats` (a bool) as the `hist_type` argument, which meant we were updating either `rocksdb.db.get.micros` (`hist_type == 0`) or `rocksdb.db.write.micros` (`hist_type == 1`) with wrong data.
Closes https://github.com/facebook/rocksdb/pull/2666

Differential Revision: D5520384

Pulled By: ajkr

fbshipit-source-id: 2f7c956aec32f8b58c5c18845ac478e0230c9516