Summary:
Added new statistics in CompactionJobStats to keep track of
deletion entries and the expiration of those entries. Updated these
fields in compaction_job.cc as compaction took place and wrote a new
test in compaction_job_stats_test.cc to verify accuracy.
Test Plan:
Wrote new test DeletionStatsTest in
compaction_job_stats_test.cc to verify
Reviewers: sdong, igor, yhchiang
Reviewed By: yhchiang
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D41355
8bca83e5dd