When extra spacing needs to be added between words for text justification, WidthIterator (and the complex text implementations) distribute the extra space very unevenly: all word spaces but the last get the same number of pixels added to them, and the last space takes the remainder. See the URL for an example where all spaces are 16 pixels wide except the last one, which is only 10 pixels wide. This may even be a regression (but a very old one).
<rdar://problem/7752961>
Created attachment 50684 [details] Sketch of fix Need to do this in the complex text code paths. Can save one roundf() per space by caching the result.
Created attachment 58622 [details] Distribute justification padding more evenly
Comment on attachment 58622 [details] Distribute justification padding more evenly r=me. I would, however, prefer at sentence independent from the file listing in the changelog that gives the gist of the change.
Fixed in <http://trac.webkit.org/projects/webkit/changeset/61128>.
http://trac.webkit.org/changeset/61128 might have broken Qt Linux Release
Yup. Looks like the test fails on Qt.