Summary:
Evict oldest blob file and put it in obsolete_files list when close to blob db size limit. The file will be delete when the `DeleteObsoleteFiles` background job runs next time.
For now I set `kEvictOldestFileAtSize` constant, which controls when to evict the oldest file, at 90%. It could be tweaked or made into an option if really needed; I didn't want to expose it as an option pre-maturely as there are already too many :) .
Closes https://github.com/facebook/rocksdb/pull/3094
Differential Revision: D6187340
Pulled By: sagar0
fbshipit-source-id: 687f8262101b9301bf964b94025a2fe9d8573421
37db5f3e89