Listener tried to modify its DOM in the constructor

[inureyes]

Bug

• Original code worked until Polymer 2.3.1. Since Polymer 2.4.0, Current paper-toggle-button does not work with error

Uncaught DOMException: Failed to construct 'CustomElement': The result must not have attributes

Reason

• Listener tried to modify its DOM in the constructor
• The element's attributes and children must not be inspected, as in the non-upgrade case none will be present, and relying on upgrades makes the element less usable.
• https://html.spec.whatwg.org/multipage/scripting.html#custom-element-conformance

Solution

• Can be solved by moving the listener binding to the attached.

[llowrey]

Thank you for this patch! I'm surprised this is still an issue one year later. It would be good to see a v3.0.2 that includes this fix.