Surprisingly enough, only repaintCompositedLayers() calls recursiveRepaintLayer() and repaintCompositedLayers() passes NULL rect. It means that we never partially paint these layers.
Created attachment 234052 [details]
This was certainly used at some point. What's the history of this code?
FrameSelection code used to call repaintCompositedLayers() with a non NULL rect. That code got heavily refactored and now it calls ::repaintUsingContainer()
Comment on attachment 234052 [details]
Clearing flags on attachment: 234052
Committed r170590: <http://trac.webkit.org/changeset/170590>
All reviewed patches have been landed. Closing bug.