https://trac.webkit.org/changeset/246694 made it so that WebPageProxy would set m_mayHaveUniversalFileReadSandboxExtension to true only if the sandbox extension to '/' is successfully created.
As shown in rdar://problem/52357508, this causes some breakage.
Created attachment 373724 [details]
Comment on attachment 373724 [details]
Clearing flags on attachment: 373724
Committed r247272: <https://trac.webkit.org/changeset/247272>
All reviewed patches have been landed. Closing bug.