Improve accessibility window title behavior

Un-reverts ag/1057448, but uses a version of Resources#getText
that returns null rather than throw an exception when no title
is available. This is the same call made before, so this change
should be safer.

Bug: 28744278
Change-Id: I8c123f4f6d74f796ab9e8ffcf955aaf881770da1
4 files changed