Update WebKit IDL Parser/Generator/Files for void -> undefined spec change - https://github.com/heycam/webidl/commit/02abd629eb80a99d7c0687eca1f3dea1ca5ac0a2.
Dupe of https://bugs.webkit.org/show_bug.cgi?id=215514 ?
Yep. *** This bug has been marked as a duplicate of bug 215514 ***