Move unload handling to a separate method
Move unload handling to a separate method

Instead of calling setCookie() directly on the unload handler, move it
to a separate unload handler method where we can do more stuff if
needed... like fire an unload beacon, for example.

forcedotcom/kylie,levexis/boomerang,FredXue/boomerang,levexis/boomerang,forcedotcom/kylie,sdgdsffdsfff/boomerang,lognormal/boomerang,sdgdsffdsfff/boomerang,lognormal/boomerang,FredXue/boomerang