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 <[email protected]>
Tested-by: Paul Stewart <[email protected]>
Commit-Queue: Paul Stewart <[email protected]>
1 file changed