Fix region sampling for secure layers

We were swapping a couple of boolean params when requesting
screenshots for region sampling, breaking region sampling for
secure layers in the process. Fix this by passing flags instead of
booleans in a long list of arguments and add a test to verify the
code path.

FLAG: EXEMPT bugfix
Fixes: 348944802
Test: presubmit
Change-Id: I58f12e5cf81cb59115c1b9c500ac1e18a8ec72e5