Also making some more state const. Instances of this class are currently constructed and used on the "worker thread" but as part of the work for bug webrtc:11993, the instances will be moved over to the network thread. Since the class as is does not require synchronization, that is a good property to make explicit now and then make sure we maintain it in the transition. Bug: webrtc:11993 Change-Id: Id587a746ce0a4363b9e9871ae1749549f8ef3e24 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/202681 Commit-Queue: Tommi <tommi@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33035}