[BUG] screencast tests fail on Mac10.14

[aslushnikov]

Offending patch: 791443d
Failing tests: https://devops.aslushnikov.com/flakiness2.html#branch=master&browser=webkit&platform=Darwin+10.14&timestamp=1620322239924

[aslushnikov]

This is fixed now. We discussed #6445 with Yury and decided to keep the frontend approach since its tiny.