Disable ParserSync test in GC stress mode for now.

R=jkummerow@chromium.org
TEST=cctest/test-parsing/ParserSync

Review URL: https://codereview.chromium.org/14075017

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14376 ce2b1a6d-e550-0410-aec6-3dcde31c8c00