As of the latest Canary build (v70), Chrome OS now has network file shares enabled by default. SMB sharing was previously possible via a flag that was added back in March, although it was quite unstable at that time. It should hopefully perform better now, allowing you to add a file share service such as Samba.
Chrome evangelist François Beaufort announced the news on Google+ and linked to the relevant Chromium Gerrit, adding that it makes viewing a shared folder pretty easy when you've gone through the setup process. To mount a shared drive, all you'll need to do is head to the settings and find "Network File Shares." Adding one is then as simple as inputting the URL and your authentication details.
This will be a great addition for many power users and comes on the back of Google releasing its own Android Samba client. That seems to have disappeared from the Play Store now, but the open source code is still on GitHub and you can still get it on APKMirror. That made Windows file shares available in the Android files app, and now Chrome OS is following suit.
- François Beaufort