Remove useless comments and properly test frame values. Also rename the FakeScreenCastStream to TestScreenCastStreamProvider. Bug: webrtc:13429 Change-Id: I9b1943f0903101a1d9228cded541d3766879d84f Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/279740 Reviewed-by: Alexander Cooper <alcooper@chromium.org> Commit-Queue: Jan Grulich <grulja@gmail.com> Cr-Commit-Position: refs/heads/main@{#38450}