Chrome Version: 59.0.3071.115 (Official Build) unknown (64-bit)
OS: Linux

What steps will reproduce the problem?
(1) chrome --user-data-dir=/tmp/empty
(2) Visit https://chromium-review.googlesource.com/c/533641/
(3) Sign in, and goto settings and change the diff font size to 10

What is the expected result?

All underscores are rendered.

What happens instead?

Underscores aren't shown.

Note that I'm using the default (I think) settings in Chrome for fonts.  In particular, The fixed width font is set to Monospace.

The default diff size in gerrit is 12, and underscores are displayed correctly.  But when I change the size to 10, the underscores disappear.

A workaround is to change the fixed with font to Noto Sans or something else other than Monospace.  (I think Deja Vu Sans Mono also has the display problem.)