WebProcessPool::notifyPreferencesChanged() is unsafely called on a background thread.
<rdar://problem/63876652>
Created attachment 400921 [details] Patch
Comment on attachment 400921 [details] Patch Thanks for fixing this! R=me.
Created attachment 400938 [details] Patch
Committed r262497: <https://trac.webkit.org/changeset/262497> All reviewed patches have been landed. Closing bug and clearing flags on attachment 400938 [details].