This was removed in https://github.com/w3c/web-platform-tests/commit/4000ca06f84efa96789a4f3493eed330399da402 I suspect we don't need it either because the default value of allowDisplayOfInsecureContent is false in WebKit and WebKitAllowDisplayingInsecureContent does not seem to exist (any more?) in the source.
Created attachment 313617 [details] Patch
Comment on attachment 313617 [details] Patch Clearing flags on attachment: 313617 Committed r218700: <http://trac.webkit.org/changeset/218700>
All reviewed patches have been landed. Closing bug.