Extending HTMLCanvasElement in Custom Element issue

Hello. My issue is described there
<http://stackoverflow.com/questions/28985426/extending-htmlcanvaselement-in-custom-element-issue>
 .

But I did not solve its fully. Why can not I create a pure custom canvas
element with a full functionality like in my example code?

-- 
*С уважением*
*Кирилл Халитов*