Add a new helper, in the viewer, to close everything during testing

[Snuffleupagus]

This has two advantages, as far as I'm concerned:

• The tests don't need to manually invoke multiple functions to properly clean-up, which reduces the risk of missing something.
• By collecting all the relevant clean-up in one method, rather than spreading it out, we get a much better overview of exactly what is being reset.

[Snuffleupagus]

When this reaches mozilla-central, we should be able to replace https://searchfox.org/mozilla-central/rev/b11735b86bb4d416c918e2b2413456561beff50c/toolkit/components/pdfjs/test/head.js#49-50 respectively https://searchfox.org/mozilla-central/rev/b11735b86bb4d416c918e2b2413456561beff50c/dom/security/test/csp/browser_pdfjs_not_subject_to_csp.js#55-56 with await viewer.testingClose() to clean-up everything there as well.

[Snuffleupagus]

/botio integrationtest

[moz-tools-bot]

From: Bot.io (Linux m4)

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Received

Command cmd_integrationtest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.241.84.105:8877/4f909edbd4b36de/output.txt

[moz-tools-bot]

From: Bot.io (Windows)

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Received

Command cmd_integrationtest from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.193.163.58:8877/d5b189e3649fdcc/output.txt

[moz-tools-bot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/4f909edbd4b36de/output.txt

Total script time: 7.71 mins

• Integration Tests: Passed

[moz-tools-bot]

From: Bot.io (Windows)

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Failed

Full output at http://54.193.163.58:8877/d5b189e3649fdcc/output.txt

Total script time: 18.76 mins

• Integration Tests: FAILED

[timvandermeij]

Looks good to me; thanks! We only need to make sure that we have a follow-up for mozilla-central: once this lands there the existing unbindWindowEvents calls will likely behave differently because we don't call the global abort controller anymore, which is now moved out into the new testingClose API.

[calixteman]

LGTM. Thank you.