Flush writebooster along with manual_gc

If WB has lots of data, we should flush them by IdleMaint.

Bug: 179030981
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
Change-Id: Ib04a8c5f8b7153f2afe88b636415accbbf27c4f8
1 file changed