I first noticed this with a local build of Chromium 54.0.2809.0, and was able to bisect this issue to https://chromium.googlesource.com/chromium/src/+log/efaf1b116773bbbc1b5e77358171f8c8d6b6b771..23fff35c8f6011affb8c3025b5e4ec3e82c13bb0 . As a result it seems this is most likely related to https://codereview.chromium.org/1939203002/ .

The issue is that if I open Chromium (after the above range, release 52 and later have this range), go to fontconfig.org (the site doesn't really matter), inspect some body text on that page, use the inspector to add 'font-family: Nimbus Sans L;' to the element style (I have this font installed) the font metrics appear to update (the line height seems to change) but the actual font and glyphs do not. According to the inspector the font initially chosen was Times New Roman, which is the current standard and standard serif font. If I perform these same actions before the above range then the font changes as expected to Nimbus Sans L when adding the above css to the element style.