Demonstrates use of matchers and WaitUntil to have tests that are more
understandable during failure.
Drive by changes,
* Remove the `const` on RTCStats.id_ as to allow for the implicit copy
constructor.
* Add [[nodiscard]] to WaitUntil as it is not useful without checking
the return value.
Bug: webrtc:381524905
Change-Id: I379910ce0fc8d9d81c96b8f164aa5a040637c85a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/370802
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Auto-Submit: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43599}
29af9f0c87