Created attachment 184896 [details] Comparison of Chrome and Safari Chrome doesn't support "image-rendering: -webkit-optimize-contrast" which causes the zoomed layout test diff view to render poorly (see the attached comparison).
It's an issue specific to Google Chrome so you should be using Chrome's bug tracker: http://code.google.com/p/chromium/issues/list Though this issue has been put on the sidelines for well over a year now, so I don't like your chances.