Summary:
This diff adds CompactOnDeletionCollector in utilities/table_properties_collectors,
which applies a sliding window to a sst file and mark this file as need-compaction
when it observe enough deletion entries within the consecutive keys covered by
the sliding window.
Test Plan: compact_on_deletion_collector_test
Reviewers: igor, anthony, IslamAbdelRahman, kradhakrishnan, yoshinorim, sdong
Reviewed By: sdong
Subscribers: maykov, dhruba
Differential Revision: https://reviews.facebook.net/D41175
