Copying a MIME type map from the UI process to the WebContent process on startup is not needed anymore, since r258891 will map the Launch Services database in the WebContent process.
Created attachment 397694 [details] Patch
Created attachment 397699 [details] Patch
Committed r260769: <https://trac.webkit.org/changeset/260769> All reviewed patches have been landed. Closing bug and clearing flags on attachment 397699 [details].
<rdar://problem/62464920>
rdar://problem/60714318
Re-opened since this is blocked by bug 211578