PlzDedicatedWorker: Add and record a new WebFeature

This CL adds WebFeature, kWorkerControlledByServiceWorkerOutOfScope,
and counts the number of dedicated workers that will not be controlled
by a service worker after PlzDedicatedWorker is enabled.

Also adds/updates tests:
- to check if WebFeature kWorkerControlledByServiceWorkerOutOfScope is
counted when a worker becomes out-of-scope although it used to be
controlled by a service worker.
- to check if worker loading is intercepted by a service worker.

Bug: 1186117
Change-Id: Ia14b05606430921da36a54e5dd5f4c0a7538f5fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2744568


Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Asami Doi <asamidoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#864935}