For use counters, we may have to add test cases to confirm use counts on a service worker are propagated to controlled shared workers in LayoutTests/http/tests/serviceworker/usecounter.html.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9996ac8918c962212f2bac8dadfb3b250cb50c61

commit 9996ac8918c962212f2bac8dadfb3b250cb50c61
Author: Hiroki Nakagawa <nhiroki@chromium.org>
Date: Wed Oct 31 05:41:12 2018

ServiceWorker: Modernize http/tests/serviceworker/usecounter.html using async/await etc

This is a mechanical cleanup CL for making it easier to add new use counter tests.

Bug:  900444 
Change-Id: Ib8d3c708c0f6ed1fd00b00bbcc9e873097cccd64
Reviewed-on: https://chromium-review.googlesource.com/c/1308240
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604166}
[modify] https://crrev.com/9996ac8918c962212f2bac8dadfb3b250cb50c61/third_party/WebKit/LayoutTests/http/tests/serviceworker/usecounter.html

Reg c#2, looks like use counter propagation from service workers to controlled dedicated workers and shared workers hasn't been working regardless of PlzWorker. See issue 901609 for details.

Hmmm... seemingly I misunderstood the behavior.

> ServiceWorkerProviderHost::CompleteSharedWorkerPreparation() is never called when PlzWorker for shared workers is enabled because script loading is handed over from the browser process to the render process before it's called from SharedWorkerScriptLoader::OnComplete().

SharedWorkerScriptLoader::OnComplete() is called even after script loading is handed over, while SharedWorkerScriptFetcher::OnComplete() is never called. Therefore, the provider host for a shared worker correctly gets execution-ready. I confirmed this by adding CHECKs in ServiceWorkerProviderHost::CompleteSharedWorkerPreparation().

Based on the observation (c#4), let me close this issue...