While it is possible to resize fonts in:
Control center-> appearence -> fonts
This has no effect on the font size used in the browser location bar !?
Changing fonts->details->dpi has also no effect on Location bar font size !?
Is this font size hardcoded in the Chromium Browser ?
I am using Chromium 48.0.2564.116 Ubuntu 16.04 (64-bit)
You can change the font sizes in the settings menu, click on advanced settings (once in settings!) and fonts setting will also show!. 
Sorry wolfman, wich settings do you mean ?
The current settings provided in Ubuntu Mate 16.04 control center->appearence->Fonts do not have influence on the font size in the Chromium address/location bar. 
Chromium Browser > Settings > Advanced Settings > Web content > Font sizes/Customise fonts:
Thank you, that setting works nice, but only for web page content.
It does not work for the original problem described in the headline.
I wrote a bug report on Chromium:
https://bugs.chromium.org/p/chromium/issues/detail?id=594491
So its one of about 6000 prio 3 Chromium bugs, might be resolved in 2018 ?
Yes, Chromium doesnt respect system DPI settings.
The report is now merged with another bug-report.
Currently the font-size in browser location bar is really hard-coded 
https://bugs.chromium.org/p/chromium/issues/detail?id=550583#c3