Bug 1487339 [wpt PR 12754] - Refactored usage of XHR, added error handling., a=testonly

Bug 1487339 [wpt PR 12754] - Refactored usage of XHR, added error handling., a=testonly

Automatic update from web-platform-testsRefactored usage of XHR, added error handling.

- Added error handling as suggested in https://github.com/web-platform-tests/wpt/pull/12162
- changed XHR calls to FetchAPI
- changed async tests to Promise tests
- corrected the existing redirect tests and reported bug: crbug/872285
- removed Same-Site and Cross-Origin XSLT tests as they seemed to fail because loading
    cross origin xslt is not supported "Unsafe attempt to load URL from frame"
    (No idea why they passed before)
- added two test cases for multiple redirects. The idea is that the Sec-Metadata header
    should be "downgraded" to less secure and should carry the value to the end.
    If a cross-origin domain controls a redirect at any point of the redirect chain,
    then the final requests are potentially influenced by the attacker.
    - (Same-Origin -> Cross-Site -> Same-Origin -> Same-Origin) -> site=cross-site
    - (Same-Origin -> Same-Site -> Same-Origin -> Same-Origin) -> site=same-site

Change-Id: I591af1948cc1f16e3b5c44f51020149e43fc2746
Reviewed-on: https://chromium-review.googlesource.com/1193953
Commit-Queue: Maciek Trzos <mtrzos@google.com>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587556}

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wpt-commits: 241cb914b6eae52ce48ad26df7d5b8c2e7088613
wpt-pr: 12754