Bug 1512134 [wpt PR 14373] - WPT: service worker: fix test for CSS ba…

…se URL., a=testonly

Automatic update from web-platform-tests
WPT: service worker: fix test for CSS base URL.

The existing test was asserting the opposite of the standard,
which is to use the response URL. See
whatwg/fetch#146.

This CL does the following:
- Tests that a CSS stylesheet fetched via respondWith(fetch(responseUrl)
  uses responseUrl as its base URL.
- Tests that a CSS stylesheet fetched via respondWith(new Response())
  uses the response URL (which is the request URL) as its base URL.
- Changes the test to not test cross-origin stylesheets. That is more
  complex than needed for this test, and there is talk of making
  subresource requests from opaque stylesheets skip the service worker,
  which would render the test ineffective for testing base URL.
- Changes the test to use waitUntil() in the message event to try
  to ensure the service worker stays alive between the message and
  fetch events.

Bug: 911974
Change-Id: I167dfe86986ec718a50d512f862f1eb49889608b
Reviewed-on: https://chromium-review.googlesource.com/c/1362776
Commit-Queue: Matt Falkenhagen <falkenchromium.org>
Reviewed-by: Ben Kelly <wanderviewchromium.org>
Cr-Commit-Position: refs/heads/master{#614277}

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wpt-commits: 3e60f8f48ebed7895b6d58a88d35ccb5a80ed3c6
wpt-pr: 14373

UltraBlame original commit: 6853099d97952c5f90ad15cb41bf48ef979c4e13