- Only "hot" user input -- i.e, freshly typed password starting
from an empty string, with keyboard focus still in the edit
box -- can be revealed.
In particular, prefilled passwod (from cached value) cannot be
revealed.
- Once keyboard focus moves out of the password edit box, the inpit has
to be deleted for the reveal feature to get re-enabled.
Signed-off-by: Selva Nair <selva.nair@gmail.com>