Can't bind to the value of a custom element that extends <input> #186

http://jsbin.com/uhipam/1/edit

In the above example I can't bind to the value property in the custom element that extends <input>.

From @rafaelw:

Looks like at least part of the problem is that Polymer isn't inspecting the element's super class. It's just calling HTMLElement directly (and by-passing the binding behavior of HTMLInputElement): https://github.com/Polymer/polymer/blob/stable/src/bindMDV.js#L72