Patch forthcoming.
Created attachment 319535 [details] the patch
Created attachment 319536 [details] the patch
Comment on attachment 319536 [details] the patch Myles assures me that he r+'d it.
Landed in https://trac.webkit.org/changeset/221450/webkit
<rdar://problem/34694106>
Migrated to https://github.com/gpuweb/WHLSL/issues/204