UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10323.46.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.107 Safari/537.36
Platform: 10323.46.0 (Official Build) beta-channel cave

Steps to reproduce the problem:
Minimal test case and explanation here:

https://stackoverflow.com/questions/49166211/cannot-catch-file-webrequest-in-chrome-extension-on-chromebook 

What is the expected behavior?
See link above.

What went wrong?
See link above.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 65.0.3325.107  Channel: beta
OS Version: 10323.46.0
Flash Version: 

As mentioned in the link, it's only a problem on ChromeOS.