Going to try and sort this out. UI is likely to change but shouldn't be too hard to get minimal functionality.

So there is not actual "done" event. We just switch the button to being open which has accessibility info attached to it. I think this is probably sufficient to understand what's happening (but I'm also not an expert on accessibility so don't know what convention is)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ebf49e00690e8812efa7deeb58fcf0a126ed2687

commit ebf49e00690e8812efa7deeb58fcf0a126ed2687
Author: yfriedman <yfriedman@chromium.org>
Date: Fri Mar 31 14:13:32 2017

Announce 'adding' accessibility event when adding a homescreen shortcut.

Provides indication that the event is actually taking place.
BUG=684596

Review-Url: https://codereview.chromium.org/2785223002
Cr-Commit-Position: refs/heads/master@{#461114}

[modify] https://crrev.com/ebf49e00690e8812efa7deeb58fcf0a126ed2687/chrome/android/java/src/org/chromium/chrome/browser/infobar/AppBannerInfoBarAndroid.java

Sam: can you run this by accessibility reviewer?

Hey Laura, is switching the label on a button sufficient for alerting?