Just for grins, I compiled the Dart app I'm working on now with --minify. It went from 530K to 240K. Then I cleared the --minify flag and used the Closure Compiler but it failed with errors. Not sure what is going on yet, but I don't think this is necessary or advisable -- I've never read of anyone using the Closure Compiler with Dart. Here is a sample few lines from --minify. It's fairly minimal.

function I(){} init() var $=I.p var $$={}