It looks like the bug only happens with NetworkService on.

Yes looks like a shadow page issue.

Usually when NeworkService is on, requests from the renderer go through throttles via:
1. (frames) RenderFrameImpl::WillSendRequest calls
  extra_data->set_url_loader_throttles(
      render_thread->url_loader_throttle_provider()->CreateThrottles(
          routing_id_, request, resource_type));
2. (dedicated & shared workers) WebWorkerFetchContextImpl::WillSendRequest calls
  extra_data->set_url_loader_throttles(throttle_provider_->CreateThrottles(
        ancestor_frame_id_, request, WebURLRequestToResourceType(request)));
3. (service workers) ServiceWorkerFetchContextImpl::WillSendRequest calls
    extra_data->set_url_loader_throttles(throttle_provider_->CreateThrottles(
        MSG_ROUTING_NONE, request, WebURLRequestToResourceType(request)));

But for requests from the shadow page, we get to WorkerShadowPage::WillSendRequest which doesn't set up throttles. And WorkerShadowPage is in blink so doesn't have easy access to content::URLLoaderThrottleProvider.

So to fix this we either need to remove the shadow page or plumb URLLoaderThrottleProvider to blink.

Shared workers seem to work probably because PlzSharedWorker does the request from the browser.

falken@: Do you think we should prioritize removing the shadow page? The issue for the shadow page is P2, but this is P1.

Not too sure. I might be able to onion soup URLLoaderThrottleProvider to make it work with the shadow page, but I'm not sure it's worth the effort if the shadow page will be removed anyway. On the  other hand, the worker fetch contexts probably need to be onion souped anyway, so URLLoaderThrottleProvider eventually will need onion souping...

How far off are we from removing the shadow page? Is it possible to happen by M73 or M74?

Ah, we might be able to hook in throttles using the shadow page's service worker network provider at WebServiceWorkerNetworkProviderImpl::WillSendRequest.

> How far off are we from removing the shadow page? Is it possible to happen by M73 or M74?

To remove it, we need to make off-the-main-thread (OTMT) service worker script fetch available. For M73, I don't think we can finish it. For M74, it would still be hard even if we'll focus only on it. We haven't shipped even OTMT dedicated worker script fetch yet that is easier than OTMT service worker script fetch...

Thanks, I think we can do this without more onion soup or removing shadow page after all.

Removed the dependency on issue 538751 (removing worker shadow page) based on c#8.