iron-input should implement IronFormElementBehavior

[zboralski]

<input is="iron-input"...> doesn't implement IronFormElementBehavior and isn't registered by iron-form as a custom elements and iron-form's validate() assumes the extended native element should have already been validated.

Ref: issue.

[notwaldorf]

For repro steps, here's a jsbin with this issue: http://jsbin.com/zadoje/edit?html,output.

I think the solution isn't to add IronFormElementBehaviour to this (as explained in #64 this will double submit inputs), but to have iron-form do the right thing (i.e. look through the form.elements array and see which ones are custom elements`).

I will take a look this week.

[notwaldorf]

Closing, as this isn't the right fix for the element (the issue is in iron-form)