Floats Don't Overhang Their Block Formatting Context Per http://www.w3.org/TR/CSS2/visuren.html#float-position: "References to [the elements] in the [rules that govern the behaviour of floats] refer only to other elements in the same block formatting context as the float." This means we don't need to look for intruding or overhanging floats in boxes that establish a new block formatting context. I couldn't find a test where we failed this rule but we do appear to be doing unnecessary work in rebuildFloatsFromIntruding() so make sure we avoid adding floats from different block formatting contexts.
Created attachment 243007 [details] Patch
Comment on attachment 243007 [details] Patch r=me
Comment on attachment 243007 [details] Patch Clearing flags on attachment: 243007 Committed r177308: <http://trac.webkit.org/changeset/177308>
All reviewed patches have been landed. Closing bug.