Idle API Tester per Paul Morris

This addon is experimental and not for general use. It was created to help Firefox developers by making this bug more visible: https://bugzilla.mozilla.org/show_bug.cgi?id=1383244

Namely, to make it more obvious when the idle timeout does not happen as expected when an add-on is using the WebExtensions idle API: https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/idle

This extension shows an "all's well" notification when the idle state changes to active. If something went wrong and idle timeout did not happen as it should have, then no notification is shown. That is because with this bug the idle state never becomes inactive, so it never changes back to active (because it is already/still active), and thus there is no notification.

This add-on also logs changes to idle state to the console with a time stamp. This is another way it makes the occurrence of this bug more visible, and thus easier to diagnose.