From the mailing list:

Got the "Deploy Polymer App" functionality to work in a new polymer app:

1. create new polymer application
2. modify build.dart:

import 'package:polymer/builder.dart';
        
main() {
  build( entryPoints: ['web/test_polymer.html', 'web/clickcounter.html']);
}

3. add library line to clickcounter.dart. e.g.:

library clickcounter;

4. add library line to main dart file:

library main;

5. right click on main html file and select "Deploy Polymer App"
6. right click on main html file in the "out" directory created in the previous step, select "Run as JavaScript"
7. you're running your polymer app as javascript!