1589252 - Add regression tests for a11y panel telemetry collection.

Status: NEW

(DevTools :: Accessibility Tools, task)

Description

[Yura Zenevich [:yzen] (please use "needinfo")]

Posting Chris' comment from (https://phabricator.services.mozilla.com/D49435) here:

At this point I would like to note that it is recommended that permanent collections all be covered by regression tests. When probes expire they are either examined and renewed or they stop collecting. But when probes are permanent, we aren't encouraged to occasionally examine them. So they can break without warning, and often without being noticed until it ships all the way to release. As such, consider adding to this bug (or filing a follow-up) some patches that exercise the collection code and examine that the expected collections happen (( There are functions in TelemetryTestUtils that make this easier. )).