I am not sure what change caused it, or if this is the first instance of flakiness:
The test itself was added in http://trac.webkit.org/changeset/82252.
Some change sets that look suspicious:
It's not due to (82681,82685], it started to flake on chromium bots like a month ago with the same text diff.
See also http://code.google.com/p/chromium/issues/detail?id=75121.
... and it doesn't fail uniformly in subsequent runs on SL WK2.
I am going to add styles-add-blank-property.html to the mac-wk2 skipped list, since it is flaking again:
Added to the mac-wk2 skipped list in http://trac.webkit.org/changeset/83481
This test has been stable lately, and is absent from the Mac-WK2 Skipped list at the moment.