[ServiceWorker] Add WPT tests to check request header for update

Spec requires that during the update of service workers, request headers
for fetching main scripts should include "Service-Worker" field, while
that for fetching importScripts() resources should not.
This patch adds WPT tests to validate this behavior.

Change-Id: I24949fd0b375f6b811a73ce24aae87a4ea7c234f
Reviewed-on: https://chromium-review.googlesource.com/c/1267297
Commit-Queue: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599126}
3 files changed