It seems like the garden-o-matic isn't going back very far in time. Example: the current screen (as of 13:45 on 12/18/2011 PDT, ~r97788) shows test failures going back 4 hours, and then a few un-timestamped tests at the bottom, including fast/selectors/visited-descendant.html . If you click through to that test on the flakiness dashboard, it shows that the test started failing about 8 hours ago, and then clicking through from that shows that the test was added in http://trac.webkit.org/browser/?rev=97745). For reference, the archived results under http://build.chromium.org/f/chromium/layout_test_results seem to go back about a week.
changing the title for the bug to be more appropriate (?)