Chrome Version:  51.0.2704.29 beta
Chrome OS Version: 8172.16.0
Chrome OS Platform: Chell DVT1

Please specify Cr-* of the system to which this bug/feature applies (add
the label below).

Steps To Reproduce:
(1) Plug in a Nexus 5X or 6P using a C to C cable or a C-to-A cable (cable type doesn't seem to matter)
(2) On Android device, from the notification pulldown, switch from Charging to File Transfer mode.
(3) Check on Chromebook, files app.

Expected Result:
Android device appears in file viewer app. Can browse files.

Actual Result:
Does not appear.

How frequently does this problem reproduce? (Always, sometimes, hard to
reproduce?)
Always.

What is the impact to the user, and is there a workaround? If so, what is
it?
File transfer doesn't work.

Please provide any additional information below. Attach a screen shot or
log if possible.

Used to work on M50, definitely. Doesn't work on 51 Beta or 52.

Tried this on Chell and Samus. Both fail.