Input type=range is not drawn. All that is required is to activate theme drawing code for this widget. I've attached a proposed patch. I'm not putting this up for review yet, because there are still issues: some tests fail because because of what seem like theme-dependent sizing issues. I'm looking for input on why this might be happening.
Created attachment 56813 [details] Functional patch
Created attachment 58088 [details] Patch
Created attachment 58089 [details] Slider support (correcting typos in the ChangeLog)
Comment on attachment 58089 [details] Slider support (correcting typos in the ChangeLog) r=me
Committed r60805: <http://trac.webkit.org/changeset/60805>