Anchor crouton position in Nearby

We're using Crouton library to display toasts when
the Nearby feature encounters errors.
Since we moved to an action bar that can be overlaid
those croutons were a bit too low, showing a gap
between the action bar and the top of the crouton.

Also added missing contentDescription in layout file.

Change-Id: I15b825f4933e425d7a0b5992fa1a1d270b2b6475
Merge "Anchor crouton position in Nearby"