This reintroduces the WARNING log level of a previous CL [1], via a default-off config flag. [1] https://webrtc-review.googlesource.com/c/src/+/148528 Bug: None Change-Id: Ica8583cbb24a1611cfc684ae02d5a0f582004024 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/156566 Commit-Queue: Sam Zackrisson <saza@webrtc.org> Reviewed-by: Per Åhgren <peah@webrtc.org> Cr-Commit-Position: refs/heads/master@{#29489}