Replacing with std::map and webrtc::flat_map where applicable. Bug: webrtc:12689 Change-Id: Id0fdb88bd3d52957b1616911eb487fc581d3b7d8 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/229182 Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Commit-Queue: Victor Boivie <boivie@webrtc.org> Cr-Commit-Position: refs/heads/master@{#34797}