It did not time out up to r246269, but times out every run on the bot since r246278, so a change in between must have slowed things down.
Created attachment 395352 [details] Patch
Committed r259448: <https://trac.webkit.org/changeset/259448> All reviewed patches have been landed. Closing bug and clearing flags on attachment 395352 [details].
<rdar://problem/61247880>