Because some hardware encoders may not preserve capture timestamp, use rtp timestamp as a key to capture time storage and restore corrupted capture timestamps whenever possible. Bug: webrtc:8497 Change-Id: Ib3449313c65e864a89cd645a3f5dec99aa9cf8e4 Reviewed-on: https://webrtc-review.googlesource.com/23620 Reviewed-by: Erik Språng <sprang@webrtc.org> Reviewed-by: Magnus Jedvert <magjed@webrtc.org> Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20732}