[JSC] unshift / shift should take structure lock
<rdar://problem/68496096>
Created attachment 408475 [details] Patch
Comment on attachment 408475 [details] Patch Nice catch. r=me
Committed r266907: <https://trac.webkit.org/changeset/266907> All reviewed patches have been landed. Closing bug and clearing flags on attachment 408475 [details].