2.0-preview issues with async imports

[valdrinkoshi]

When <paper-tabs> is imported asynchronously, the element is not correctly layout.
http://jsbin.com/taqotul/7/edit?html,output

[Tundon]

@valdrinkoshi I believe the issue is because the polymer.html is imported async. If you had imported polymer.html up front, <paper-tabs> would work correctly whether imported async.

[valdrinkoshi]

It should be possible to load asynchronously dependencies. In the example I'm loading paper-tabs import only, which synchronously load polymer.html.