dart2js OldEmitter: Change to named holes in js output strings plus some extra clean-ups.

R=floitsch@google.com

Review URL: https://codereview.chromium.org//828753002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42572 260f80e4-7a28-3924-810f-c04153c831b5