<link rel=preload> must have a valid `as` value error on Chrome console

[andrewspy]

Description

When browsing https://hn-polymer-2.firebaseapp.com on Chrome (v64, Windows). there are 3 similar warnings on:-

<link rel=preload> must have a valid `as` value

Expected outcome

No warning on Chrome console.

Actual outcome

3 similar warnings on:-

<link rel=preload> must have a valid `as` value

Live Demo

https://hn-polymer-2.firebaseapp.com

Steps to reproduce

1. "Clear sites data" on Chrome under "Application" > "Clear Storage".
2. Visit https://hn-polymer-2.firebaseapp.com

Browsers Affected

• [x] Chrome
• [ ] Firefox
• [ ] Safari 9
• [ ] Safari 8
• [ ] Safari 7
• [ ] Edge
• [ ] IE 11
• [ ] IE 10