platform/mac/fast/scrolling/scroll-select-bottom-test.html is failing on Mavericks, maybe after http://trac.webkit.org/changeset/171891 though I haven't confirmed that. That change should not have affected Mavericks -- it was meant to target Yosemite, and the test seems to pass on Yosemite.
I skipped the test for now with http://trac.webkit.org/changeset/171898
Will investigate shortly.
This test is failing on Apple MountainLion Release WK1 too, updating the title.
After looking the tests over manually with Beth on all platforms, I do not think that her changes broke anything. It looks like the test was making improper assumptions on the Mavericks (and prior) platforms, and should be fixed.
With http://trac.webkit.org/changeset/171948 I skipped the tests on the platforms that we expect it to fail, based on the lack of contentInset support.