Bug 1000173 - Display User Icon in Settings When FMD is Remotely Trackin...

...g Device
After triggering the callback, we could test if `mozL10n.localize` (note that the function was "spied") is called correctly by using `assert.ok(navigator.mozL10n.localize.calledWith(trackingSection, 'findmydevice-active-tracking' ))`.