WPT: service worker: Refactor and format navigation-redirect.https.html.

In preparation for extending or modifying the test to test Client.url
and resultingClientId for whatwg/html#3891.

Bug: 876223
Change-Id: I50e8b8c21c5f8639a24a9c2ec00df3ccafdc8ac8
Reviewed-on: https://chromium-review.googlesource.com/1184656
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585738}