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}