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}
