Chrome Version: 57.0.2987.32 (Official Build) dev (64-bit)
OS: ChromeOS

What steps will reproduce the problem?
(1) Open the Files app.
(2a) Click on the hotdog dots in the top right.
(2b) Right-click on a file.

What is the expected result?

Expect that the context menu appears.

What happens instead?

Sometimes the menu appears, but often it doesn't; once it fails, it will continue to fail for that Files instance.

Looking in chrome://inspect following a failure, I see:

Uncaught TypeError: menuItem.isSeparator is not a function
    at HTMLElement.updateCommands (main_scripts.js:11042)
    at HTMLButtonElement.showMenu (main_scripts.js:11333)
    at HTMLButtonElement.handleEvent (main_scripts.js:11262)