Needed for testing in a follow-up CL. Using ToString rather than absl::StrCat because I want the name of the enum (e.g. "INVALID_MODIFICATION") as opposed to the enum value (int). Bug: none Change-Id: I45a925fad65395d1e6a886a9f787c2f360fb8604 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/374343 Reviewed-by: Evan Shrubsole <eshr@webrtc.org> Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Commit-Queue: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43777}