Protect account chooser activities against overlay.

Bug: 172841550
Test: manual
Change-Id: I1a16808426934f4a8d12410576d769443e4c2a04
Merged-In: I3cd5a94386f15cf60a7fe3095b00815e4a6485ae
(cherry picked from commit 6ff42dd2d264cd89acdf45cf403147a870a14086)
3 files changed