UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3472.3 Safari/537.36 OPR/56.0.3018.0 (Edition developer)

Example URL:
http://www.columbia.edu/~fdc/sample.html

Steps to reproduce the problem:
1. Make sure no custom font is configured
2. Open a web page that does not contain any css

What is the expected behavior?
Use a serif font (Liberation Serif was the default standard font in stable Chrome) to render the text

What went wrong?
Chromium uses FreeMono on Ubuntu.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? Yes 67.0.3396.99

Does this work in other browsers? Yes

Chrome version: 69.0.3493.3  Channel: stable
OS Version: Ubuntu 18.04
Flash Version: 

When no custom font is configured in setting, the standard font, serif font and sans-serif font are all marked as "custom". Only fixed-width font has a value (Monospace).

This is the default setting when I installed Chromium. And any sites without CSS will be rendered with FreeMono.

Also, if only a missing font is set in the CSS (ex. font-family: "Arial"), it will also be rendered with FreeMono instand of a sans-serif font.