KeyframeEffectStack::ensureEffectsAreSorted() has several areas where either null pointers or an unexpected condition could cause a crash that's further away from the actual failure. To make these issues easier to detect and troubleshoot, add several RELEASE_ASSERTs to test these cases explicitly.
Created attachment 395638 [details]
Created attachment 395647 [details]
Committed r259630: <https://trac.webkit.org/changeset/259630>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 395647 [details].