Events cleanup

[engwan]

When I navigate away from a component that's resize aware and then resize the window, I get an error:

Uncaught TypeError: Cannot read property '0' of undefined

on this line:

 return this.$()[0].getClientRects()[0];

I assume because the events are not cleaned up? Should the mixin also include a willDestroyElement hook that removes the event listeners?

Also, it's good to add a reminder to the docs to call this._super on didInsertElement if it's overriden when using the mixin. Took me a while to realize why it wasn't working.

[localpcguy]

FYI for anyone coming across this error in the future, ensure that if your component calls willDestroyElement it also calls this._super. Like the initial comment, took me a little while to realize that was why the events were not being de-registered and that then caused the initial error.

[sheriffderek]

I would probably have run into this later today! Glad I saw this. That sounds like a good thing to add to the readme. (I know - maybe you should know* this already) --- but it would be a nice reminder.