Reason for revert: Reland: downstream code expectation about rtp_sender timestamp adjusted. Original issue's description: > Revert of StartTimestamp generated randomly in RtpSender constructor (patchset #4 id:60001 of https://codereview.webrtc.org/2241193002/ ) > > Reason for revert: > Breaks downstream code. > > Original issue's description: > > StartTimestamp generated randomly in RtpSender constructor > > instead of not-randomly at SetSendingState(true) > > Renamed to timestamp_offset_ to better match meaning of the variable. > > > > R=asapersson@webrtc.org, terelius@webrtc.org > > > > Committed: https://crrev.com/4466782ae43e1b1125a55ee7e18abd10dd37cede > > Cr-Commit-Position: refs/heads/master@{#13796} > > TBR=asapersson@webrtc.org,terelius@webrtc.org > # Skipping CQ checks because original CL landed less than 1 days ago. > NOPRESUBMIT=true > NOTREECHECKS=true > NOTRY=true > > Committed: https://crrev.com/86c96948e340cf8b879bddb0c7293f3b5ad4dad4 > Cr-Commit-Position: refs/heads/master@{#13798} TBR=asapersson@webrtc.org,terelius@webrtc.org # Skipping CQ checks because original CL landed less than 1 days ago. NOPRESUBMIT=true NOTREECHECKS=true NOTRY=true Review-Url: https://codereview.webrtc.org/2257083002 Cr-Commit-Position: refs/heads/master@{#13811}