solved issue #1372 for me

I'm not sure if alle these changes are necessary to make Spark work.
At least I think they should do no harm and are according to my knowledge how to initialize Polymer.

I just wanted to check your widgets and experienced error messages when I tried to run the demo pages.
I then started to apply https://code.google.com/p/dart/issues/detail?id=17546#c14 (import polymer.html and move the script tag to the end of the body.
Then I tried to run Spark to see if my changes didn't break anything there so I can make a pull request.
Spark failed and I found #1372 and applied the same changes I made to the widgets to Spark and for me it seems to work fine. It's my first time using Spark so I don't know how to test it extensively.