In preparation for the spec moving closer to PR, let's not have placeholder metrics not implemented. Bug: webrtc:14167 Change-Id: If4688ef85b57f88154d490186b306b30414874e4 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/265383 Reviewed-by: Harald Alvestrand <hta@webrtc.org> Commit-Queue: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/main@{#37205}