Split out Function.apply named argument case

One customer benchmark is 10% faster and 2% smaller with this change.

R=floitsch@google.com

Review URL: https://codereview.chromium.org//805583002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42358 260f80e4-7a28-3924-810f-c04153c831b5