Bug 1691099 [wpt PR 27512] - Reorganize and augment beacon wpt, a=testonly

Bug 1691099 [wpt PR 27512] - Reorganize and augment beacon wpt, a=testonly

Automatic update from web-platform-tests
Reorganize and augment beacon wpt

 - Run tests on secure contexts. I'm planning to use the sec-fetch-mode
   header once WebKit supports it, which is only available on secure
   contexts.
 - Replace html files with window.js files.
 - Merge many beacon-basic-* files into beacon-basic.https.window.js.
   This is doable because the payload size limit is per context, not
   per page.
 - Merge beacon-readablestream.js and beacon-error.sub.window.js into
   beacon-basic.https.window.js.
 - Merge beacon-preflight-failure.sub.window.js into
   beacon-cors.https.window.js.
 - Add more cross origin tests in beacon-cors.https.window.js.
 - Slim down beacon-common.sub.js.

Also remove some test files in http/tests/sendbeacon, because they are
covered by wpt/beacon.

Bug: 720303
Change-Id: Id65c70d290753428d5d17bc8e9e783969ff8bc16
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2677465
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Dominic Farolino <dom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#852515}

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wpt-commits: a341862f7bf55470eb456fbdbb20e465508e7cb9
wpt-pr: 27512