The fix in https://bugs.webkit.org/show_bug.cgi?id=179129 was not completely right. We need to translate to the root view, otherwise coordinates returned are still in subframe's client coordinate system.
Created attachment 328007 [details]
Comment on attachment 328007 [details]
Clearing flags on attachment: 328007
Committed r225367: <https://trac.webkit.org/changeset/225367>
All reviewed patches have been landed. Closing bug.