making it symmetric to AbsoluteSendTime::Parse function. Bug: None Change-Id: I9c71d840768064022ebebbbeb2962aeeecc68392 Reviewed-on: https://chromium-review.googlesource.com/531044 Reviewed-by: Björn Terelius <terelius@webrtc.org> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#18555}