Yet another prerequisite for replacing RTCStatsMember<T> with
absl::optional<T>, but this looks like the last one.
Bug: webrtc:15164
Change-Id: I2cde51e8c8c951f71b48ccd45e07146091a99616
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/334647
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41541}