This CL refactors RtpSenderTest.SendPacketHandlesRetransmissionHistory, moves some testing to rtp_ender_egress_unittest and adds test coverage for a few cases. Bug: webrtc:11340 Change-Id: Ic225d2af43c3926f69fe3ea45f41b18c29b8b4fd Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/219796 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34111}