As brought up in the review comments for https://phabricator.services.mozilla.com/D43435 we really want a test to make sure that we don't accidentally break the printing telemetry. I tried creating a test along the lines of the tests in toolkit/components/printing/tests but ran into issues. Since we want to get this into ESR as soon as we can to gather some data for the printing improvement project, I've landed without a test for now. That needs to be remedied soon.