This one is frequently accessed - Mainly by ::CreateReportBlocks and is visible in performance profiles (although not very much). By using webrtc::flat_map, better data cache locality is expected. Bug: webrtc:12689 Change-Id: Ic2ebcad806788074b2b4cb244a25395a48df1852 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/232541 Commit-Queue: Victor Boivie <boivie@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/main@{#35054}