The following layout test is flaky on Mac trybots

http/tests/devtools/coverage/coverage-view.html

Probable cause:

Seemed to regress in:
https://chromium-review.googlesource.com/c/chromium/src/+/693045

See: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_tests&tests=http%2Ftests%2Fdevtools%2Fcoverage%2Fcoverage-view.html

The last line of Expected is missing:
http://127.0.0.1:8000/devtools/coverage/resources/highlight-in-source.css CSS used: 67 unused: 142 total: 209