Fix intermittent unit test failure when 2 comments collide
Using messageboxId to lock timestamp if it is a top level comment.
Merge branch 'leafTest-squashed'

* leafTest-squashed:
  Using messageboxId to lock timestamp if it is a top level comment.
  Fix intermittent unit test failure when 2 comments collide
Fixed up _lockUniqueTimestamp and added @private in its JSDoc.
Followed up on message timestamp locking