Summary:
This information has been already available as part of the `rocksdb.blob-stats`
string property. The patch adds a dedicated integer property to make it easier
to surface this information in monitoring systems.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9835
Test Plan: `make check`
Reviewed By: riversand963
Differential Revision: D35619495
Pulled By: ltamasi
fbshipit-source-id: 03fb0b228aa27d3859a1e3783bcb7eca095607f8