After evaluating <http://trac.webkit.org/browser/trunk/LayoutTests/fast/workers/resources/worker-common.js> in a worker thread, there is a leak of "evt" detected. I'm not sure why this only happened in workers, and only on a single test, but Oliver showed me how to fix this in JavaScriptCore, patch forthcoming as soon as tests are done.
Created attachment 26896 [details] proposed patch
Committed revision 40086.