... more precisely, do not mess up the exceptional edges.

Bug: chromium:924151
Change-Id: I3541a1c339c07f509519d4ece6d677dd499f181e
Reviewed-on: https://chromium-review.googlesource.com/c/1429860Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59063}