This CL is extracted from https://webrtc-review.googlesource.com/c/src/+/208584 PacketSequencer now has its own unit tests. They are maybe somewhat redundant with a few RtpSender unit tests, but will defer cleanup to a later CL. Bug: webrtc:11340, webrtc:12470 Change-Id: I1c31004b85ae075ddc696bdf1100d2a5044d4ef5 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227343 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34638}