workaround for type 'AElement' is not a subtype of type 'AElement' of 'a'

as discussed in this thread https://groups.google.com/a/dartlang.org/forum/#!topic/web-ui/8eavxm41Vtw
This gives warnings but it works.

other workarounds would require removing init.dart in index.html and using various combinations of initPolymer and Polymer.register.
But I'm sure you have seen the discussions here https://groups.google.com/a/dartlang.org/forum/#!topic/web-ui/BGWNyCA4iOI and here https://groups.google.com/a/dartlang.org/forum/#!topic/web-ui/_9c1Hw5L1xc

But as it seems this error is getting fixed in r29137/0.8.6, so feel free to reject this workaround :)