Make sure to remove message receivers before they are deallocated
Created attachment 256265 [details] Patch
Committed r186464: <http://trac.webkit.org/changeset/186464>
Seems to have caused API tests crashes: https://build.webkit.org/builders/Apple%20Mavericks%20Debug%20WK2%20%28Tests%29/builds/12956/steps/run-api-tests/logs/stdio Please take a look.