Added blur event listener and _onBlur handler

[skullerj]

Sometimes it's useful to know when the user leaves the input. You can listen this event from your paper-input for instance using on-iron-input-blur="someHandler"

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[skullerj]

I signed it!

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[notwaldorf]

This isn't needed. Since iron-input is just a native input, the native events jsut work. Here is a jsbin demoing this: http://jsbin.com/xoceha/2/edit?html,output

Basically, you can just do:

document.querySelector('input[is="iron-input"]').addEventListener('blur', function() {
  console.log('blurred!');
});