There was a test for deserialization but not serialization. This was
probably always broken and no one noticed. I only noticed while
debugging something else.
BUG=None
TBR=pthatcher@webrtc.org
Review-Url: https://codereview.webrtc.org/3012383002
Cr-Commit-Position: refs/heads/master@{#19875}
d45aea8f42