Add preference of private overlays for finding ACLs

This heuristic embodies the notion that ACLs to be used are probably
not kept in the public space unless everything is public.

BUG=chromium:336504
TEST=unittests.

Change-Id: I810fead5054dd7ee0cd5c26005b3c5aa9f31ed5e
Reviewed-on: https://chromium-review.googlesource.com/184571
Tested-by: Peter Mayo <petermayo@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Peter Mayo <petermayo@chromium.org>
2 files changed