bfcfe034f4
This prepares for deferred sequence numbering, and is (sort of) extracted from https://webrtc-review.googlesource.com/c/src/+/208584 Bug: webrtc:11340, webrtc:12470 Change-Id: I2f3695309e1591b9f7a1ee98556f4f0758de7f69 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227352 Commit-Queue: Erik Språng <sprang@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34643}