In the current theme rendering engine we get the percentLoaded() value from the player and fill the media slider track accordingly. Instead it'd be nice to get the ::buffered() TimeRanges and draw them as rectangles inside the media slider track.
Created attachment 65920 [details] proposed patch
Created attachment 65921 [details] proposed patch
Comment on attachment 65921 [details] proposed patch LGTM.
http://trac.webkit.org/changeset/66460