logd: worst uid record watermark part five

(cherry pick from commit e2827d526a4a84b02fe79e34e45b4e681eda3cd6)

A regression that resulted in increased memory consumption for some
logging patterns because we rarely did merge or leading checks, and
age-out checking. On the last prune cycle, we reset for a full scan.

Add some comments describing the pruning processes.

Bug: 23327476
Bug: 23681639
Bug: 23685592
Change-Id: I22b0f339c9269b006831fda9cefe295a263ebb92
1 file changed
tree: 91f7ab7211799da1cb42c9d47f767a17c09b9966
  1. liblog/
  2. logcat/
  3. logd/
  4. logwrapper/