Refactor flowThreadPortionOverflowRect so that it calls a helper that takes the flowThreadPortionRect and bools for first/last region. This will allow column and page sets to call the helper on a per-column or per-page basis and still have the right thing happen regarding outline inflation and clipping within the first and last columns in a set.
Created attachment 161025 [details] Patch
Landed in r127008. I just folded this into the painting bug.