Gerrit's "Set Review" API has a built-in trap:

 drafts (optional)
	How draft comments are handled that are already in the
	database but that were not also described in this input.

	Allowed values are DELETE, PUBLISH, PUBLISH_ALL_REVISIONS and
	KEEP. All values except PUBLISH_ALL_REVISIONS operate only on
	drafts for a single revision.

	If not set, the default is DELETE.

That destructive default is almost never what a person wants.  Use
KEEP instead.

Noticed because "git cl try" was losing people's comments.

Bug: gerrit:6812
Change-Id: I1d09231ea23b13c925d301241bef266df2ddf1cf
Reviewed-on: https://chromium-review.googlesource.com/764488Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Jonathan Nieder <jrn@google.com>