Bug 1733592 [wpt PR 30862] - Fix flaky coop reporting tests., a=testonly

Bug 1733592 [wpt PR 30862] - Fix flaky coop reporting tests., a=testonly

Automatic update from web-platform-tests
Fix flaky coop reporting tests. (#30862)

Previously coop reporting tests written using the
runNavigationReportingTest helper shared the same report endpoints.
This is problematic as wpt tests are executed in parallel and all
reports are sent to the same python handler. When multiple tests
uploaded coop reports and subsequently queried the handler, they
sometimes gets back reports uploaded by other tests.
Moreover, after a coop test completes the page uploads another report
for navigating away from the test webpage if a COOP policy is set. This
causes a problem for subsequent invocation of the same test as the
reports are persisted on the python handler.

This CL uses a unique reportID for each test's reporting endpoint and
uses WPT pipe substitution to pass it to test helper function. It also
resets the python handler's stored reports for that unique reportID
before a test is run so that running the tests multiple times yield the
same PASS every time.

Bug: 1249043
Change-Id: Ib5679d0d8e5da5421ac5225cc9e87029c0ffca89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3156345
Commit-Queue: Rodney Ding <rodneyding@google.com>
Reviewed-by: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/main@{#924310}

Co-authored-by: Rodney Ding <rodneyding@google.com>
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wpt-commits: 9c8389ed7bf078b82a750dbf7775c8aa59b6927e
wpt-pr: 30862