Apple does not use that Webkit branch, however. They maintain their own branch internally that cherry picks from upstream. Webkit could very well accept a patch, and then Safari never ships that patch because they disagreed with it for use in Safari.

Also, unrelated fun fact: Did you know Webkit still uses svn? That Github repo you linked to is a clone of Webkit's own git repo (git.webkit.org), which is a mirror of their actual repo (svn.webkit.org).