The test should be doing multiple rounds of mutations in a single document to test what is supposed to test (like it did before r227756).
Created attachment 332652 [details] patch
Comment on attachment 332652 [details] patch View in context: https://bugs.webkit.org/attachment.cgi?id=332652&action=review > PerformanceTests/StyleBench/resources/tests.js:5 > + steps.push(new BenchmarkTestStep(`Adding classes, step ${i}`, (bench, contentWindow, contentDocument) => { Instead of explicitly saying step, why not just `Adding classes - ${i}`. Ditto for the rest.
https://trac.webkit.org/r227850
<rdar://problem/37042601>
https://trac.webkit.org/changeset/227863