Summary: Most of the approach is copied from WebSQL's MySQL branch. It's nice that we can do this without touching core RocksDB code.

Test Plan: Compiles and runs. Didn't test flashback code, as I don't have flashback device and most if it is c/p

Reviewers: MarkCallaghan, sdong

Reviewed By: sdong

Subscribers: rven, lgalanis, kradhakrishnan, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D35391