This changed in the spec, we should just finish the script without handling the alert at all. https://w3c.github.io/webdriver/#dfn-execute-a-function-body https://github.com/w3c/webdriver/commit/afb578090bc95718debeab6a6821da8d12b952c8
Created attachment 346902 [details] Patch
Committed r234792: <https://trac.webkit.org/changeset/234792>
<rdar://problem/43219041>