See results database: https://results.webkit.org/?suite=layout-tests&test=inspector%2Fpage%2FsetShowPaintRects.html
Failures are much more common on debug builds, so I suspect there is a timing issue between the two test cases where we are still showing repaint rects from before disabling them.
Mac test expectations updated in r285727 (244186@main): <https://commits.webkit.org/244186@main>.
Flakiness is reproducible with this command:
rwt --debug inspector/page/setShowPaintRects.html --iterations 100 --exit-after-n-failures 1 --force
Pull request: https://github.com/WebKit/WebKit/pull/1541
Committed r295580 (251585@main): <https://commits.webkit.org/251585@main>
Reviewed commits have been landed. Closing PR #1541 and removing active labels.