Add strings for the screen overlay warning

We do not allow interaction with the permissions UI if
it is covered by screen overlay to prevent UI redressing
attacks. This change adds the strings for the warning
dialog we show if there is an overlay when the user tries
to interact with the permissions UI.

bug:22317719

Change-Id: Ibaa04b89b52757275dc08f228e3bf496606409fb
1 file changed