'length' property is wrong for variadic operations: https://heycam.github.io/webidl/#dfn-optional-argument The final argument of a variadic operation is also considered to be an optional argument, so we should not account for it when computing the value of the 'length' property.
Created attachment 262271 [details] Patch
<rdar://problem/22936792>
Comment on attachment 262271 [details] Patch Clearing flags on attachment: 262271 Committed r190621: <http://trac.webkit.org/changeset/190621>
All reviewed patches have been landed. Closing bug.