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

What steps will reproduce the problem?
No idea what about my zip file is provoking this.
(1) Create a zip file of a Chrome App, from source code, and upload it to Drive.
(2) Share it with a colleague who has a Chromebox.
(3a) Have them try to download the file.
(3b) Have them add the file to their Drive, then download from there.

What is the expected result?

Expect that the file can be downloaded; it's reasonable that it may be flagged as malicious, but expect that their is some way to indicate that it's OK to open, or at least to file feedback to Chrome that the warning is invalid and should be investigated.

What happens instead?

For (3a) Chrome shows a notification indicating that the file was blocked due to "not often being downloaded". There is no way to continue to download the file, just a "Learn more" link that doesn't provide any way to bypass the block nor provide feedback on it being invalid, either.

For (3b) the Files app shows a "Scanning zip file" notification, which disappears after several seconds. It neither indicates that the file is bad, nor does it open it. Clicking on the file again has no effect whatsoever.