Prepare RenderLayer/RenderLayerBacking for RenderSVGModelObject support: Include hidden SVG layers in the z-order lists for hit testing purposes
Created attachment 451015 [details] Patch, v1
<rdar://problem/88860892>
We can postpone review of this, until we have a testing infrastructure for LBSE in place -- it's too hard to review this w/o seeing a test progression. Let's delay it and clear r? flag. It does not block bug 236194.