After upgrading to Chromium 60 on current Debian Testing you might find yourself with a huge UI if you are on a HiDPI device. The current Chromium version has a bug (see Debian tracker). The proposed solution is to run Chromium with a manual scale factor setting. On a 15" MBP Retina, using
chromium --force-device-scale-factor=1.5 yields the same UI size that I was used to before the upgrade.
Looking at the Chromium upstream bug tracker, this issue is solved since end of May. It'll find it's way to Debian, eventually. In the meantime the workaround works just as well.