The test is failing after r258741: fast/dom/HTMLAnchorElement/anchor-file-blob-download-includes-backslash.html [ Failure ] r258741 sanitizes the output of suggested downloading file. For some reason, the sanitization doesn't take place in GTK.
Created attachment 402421 [details] Patch
By the way, this should also be tagged [WPE] — or [Soup] instead of [GTK][WPE].
Committed r263388: <https://trac.webkit.org/changeset/263388>