[polymer] publish -pre.12
[polymer] publish -pre.12

BUG=

Review URL: https://codereview.chromium.org//288443002

git-svn-id: 0aa7e0b98478d6ef7145d04e8154f8ab2209deba@36084 260f80e4-7a28-3924-810f-c04153c831b5

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