lorgnette: Prevent multiple instances

Normally, only a single instance of lorgnette runs at a time,
because lorgnette is launched on demand via a DBus service
file.  However, it's good to assert that this is in fac the case.

BUG=chromium:356874
TEST=Unit tests

Change-Id: I44788c9aa05075fc3d69656894b8e413041a9024
Reviewed-on: https://chromium-review.googlesource.com/195606
Reviewed-by: Ben Chan <benchan@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
1 file changed