Chrome 73.0.3669.0 Platform 11574.0.0 on eve

* Turn on ChromeVox at login screen
* Login as owner
* Go to settings > advanced > powerwash
* Start the powerwash
* Device reboots
* "Reset this Chrome device" webui dialog appears. ChromeVox orange highlight is on the dialog buttons.
* Press tab a few times
* Orange highlight moves to "Shut down" shelf button

Expected: Can use search-arrows or tab to navigate back to dialog

Actual: Tab doesn't move focus. Search-arrow moves focus within the shelf, but I can't get back to the dialog.

lprazdnik saw this (or something similar) in  issue 922086 

(fyi this happens both with and without the SingleProcessMash flag)