Add easy way for people to build/transition images

[GoogleCodeExporter]

http://html5-demos.appspot.com/static/webcomponents/index.html#40

I've hijacked the build class for this in the past, but something easier would 
be great
where you don't have to edit css.

Original issue reported on code.google.com by ericbide...@google.com on 5 Mar 2013 at 3:54