2.x class-based elements don't have behaviors defined in the constructor

[valdrinkoshi]

A legacy element (Polymer({ is: 'my-el' })) will have behaviors defined for each instance.

A class-based element (class MyEl extends Polymer.Element) will instead have behaviors defined in the constructor, so each instance must access via this.constructor.behaviors.
http://jsbin.com/fufikun/1/edit?html,console,output

How should hybrid element authors go about it?

[valdrinkoshi]

an example: PolymerElements/iron-a11y-keys-behavior#69
Should iron-a11y-keys-behavior retrieve behaviors like this?

var behaviors = this.behaviors || this.constructor.behaviors

Or should we expect Polymer to set behaviors to the instances?