Use RenderBox in volumeSliderOffsetFromMuteButton, since that's what is actually being used.
Created attachment 83573 [details]
Comment on attachment 83573 [details]
Actually, I think I can replace this whole mess with a better, cleaner mess.
Turns out better mess didn't work out. Patch coming up.
Created attachment 84615 [details]
Committed r80276: <http://trac.webkit.org/changeset/80276>
http://trac.webkit.org/changeset/80276 might have broken Windows Release (Build) and Windows Debug (Build)