The GraphicsLayer code has this method called "graphicsContextsFlipped", which is vague and not really meaningful. What we really need is an indication that the compositing system uses a top-down or bottom-up cooridinate system.
Created attachment 30308 [details] Patch, changelog
Comment on attachment 30308 [details] Patch, changelog r=me
http://trac.webkit.org/changeset/43777