Upstream service worker "XHR" test to WPT

The original version of this test would only pass if the service worker
did *not* intercept the XHR request. That behavior conflicted with the
Fetch and Service Worker specification and with the test's documentation
itself. Update the test to pass only if the service worker intercepts
the request.

In addition:

- Update URLs to suitable values for the Web Platform Tests project
- Add "use strict" directives to script bodies
- Increase precision of "cleanup" logic scheduling
- Re-name files to adhere to precent set by existing WPT tests
- Catch and report errors within Promise chain rather than relying on
  implicit reporting of uncaught errors.

BUG=688116, 602051
R=falken@chromium.org

Review-Url: https://codereview.chromium.org/2907443002
Cr-Commit-Position: refs/heads/master@{#476324}
10 files changed