Custom properties on a stylesheet don't persist, unless an explicit reference to it is kept.
Created attachment 74303 [details]
Comment on attachment 74303 [details]
From a GC footprint perspective, the approach here isn't ideal, since, as you say in your FIXME, we might artificially keep alive style wrappers we could have thrown away.
However, I expect that the set of all style-related DOM nodes in a document is quite small in practice -- and often these nodes aren't even wrapped by JS -- so in these cases I think this approach is fine.
http://trac.webkit.org/changeset/72344 might have broken SnowLeopard Intel Release (Tests)
The following tests are not passing:
A subtest changed from FAIL to PASS there. Probably for a good reason, but maybe not, hard to tell with those mega-tests.