relax DCHECK and explain when it previous version could be hit.
Use concise versions of the GetExtension functions.
Reduce scope of the `lock_`
Bug: None
Change-Id: Iafc570ffe7e5b2dcbdfe166b26b140f7959c28c7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/291711
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39246}
65ab5fd728