fix Polymer to work with latest JS interop
fix Polymer to work with latest JS interop

both places we used dart:js were broken for different reasons :). On the bright side, a huge hacky workaround is gone!

R=jacobr@google.com

Review URL: https://codereview.chromium.org//31423002

git-svn-id: 0aa7e0b98478d6ef7145d04e8154f8ab2209deba@28915 260f80e4-7a28-3924-810f-c04153c831b5

meflyup/polymer-dart,jakemac53/polymer-dart,meflyup/polymer-dart,ronlobo/polymer-dart,jakemac53/polymer-dart,dam0vm3nt/polymer-dart,ronlobo/polymer-dart,dart-archive/polymer-dart,dart-archive/polymer-dart,dam0vm3nt/polymer-dart