And allow populating network2 timestamp if we want to preserve pacer timestamp. Bug: webrtc:8853 Change-Id: I895d5ce8a9cca8ceeec3bf08e2eff02bf3b2f5fd Reviewed-on: https://webrtc-review.googlesource.com/48640 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Cr-Commit-Position: refs/heads/master@{#21937}