This gets rid of the SctpTransportMap::Retrieve method and forces everything to go through PostToTransportThread, which behaves safely with relation to the transport's destruction. Bug: webrtc:12467 Change-Id: Id4a723c2c985be2a368d2cc5c5e62deb04c509ab Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208800 Reviewed-by: Niels Moller <nisse@webrtc.org> Commit-Queue: Taylor <deadbeef@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33364}