and add a unit test
BUG=webrtc:11796
Change-Id: I8e73b22f007c15c862faad7ca881d93c14a3a46f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/184160
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/master@{#32104}