reported by Greg:
In the v8 version we're using, it seems like IdleNotification()
doesn't necessarily trigger garbage collection (by design), which
causes auto2.js to fail sometimes on my v8 builds. If we set a global
--expose-gc flag in v8 when creating the engine, there's a built-in
gc() method which forces gc that we can use for testing - the other
IdleNotification we can rename allowGC(). Is there a reason we
shouldn't do this? I've got a patch ready, seems to work.