It looks like the changes in r252161 caused 3 tests to time out on Mac and iOS: transitions/multiple-shadow-transitions.html transitions/cubic-bezier-overflow-shadow.html legacy-animation-engine/transitions/cubic-bezier-overflow-shadow.html I was able to reproduce these timeouts using command: run-webkit-tests transitions/multiple-shadow-transitions.html transitions/cubic-bezier-overflow-shadow.html legacy-animation-engine/transitions/cubic-bezier-overflow-shadow.html --iterations 20 -f They reproduce on r252161 but not r252160.
<rdar://problem/56986342>
Created attachment 383064 [details] Patch
https://trac.webkit.org/changeset/252203/webkit