When clicking on a link you will occationally trigger the two ASSERTs addHighlightRect. ASSERT(!rect.intersects(prev)); ASSERT(!rect.intersects(next)); It appears to be possible because the center-block is adjusted to the boundaries of first and last rect, after it has been tested if it intersects with first or last.
Created attachment 133770 [details] Patch
Comment on attachment 133770 [details] Patch Seems correct :-)
Comment on attachment 133770 [details] Patch Clearing flags on attachment: 133770 Committed r112077: <http://trac.webkit.org/changeset/112077>
All reviewed patches have been landed. Closing bug.