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### Issue Details

* **Electron Version:**
  * 9.1.1
  * 10.0.0-beta.4
* **Operating System:**
  * Linux x64

### Expected Behavior

Don't crash when `nodeIntegrationInWorker` is `true` and a service worker is being registered. :slightly_smiling_face:

### Actual Behavior

A crash occurs once the service worker is attempted to be registered (blank page, DevTools disconnects).

### To Reproduce

Attempt to register a service worker with `nodeIntegrationInWorker` set to `true`.

```sh
$ git clone https://github.com/lgrahl/electron-node-integration-service-worker-crash
$ npm install
$ npm start
```

Commit https://github.com/lgrahl/electron-node-integration-service-worker-crash/commit/97b14f2c599bfd25ce416b8a7ee91d9122bbfe2c
shell/browser/electron_browser_client.cc
content::RenderFrameHost* rfh,
    content::SiteInstance* pending_site_instance) {
  
  ConsiderSiteInstanceForAffinity(rfh, pending_site_instance);
  
  auto* web_contents = content::WebContents::FromRenderFrameHost(rfh);
  auto* pending_process = pending_site_instance->GetProcess();
  pending_processes_[pending_process->GetID()] = web_contents;
  if (rfh->GetParent())
    renderer_is_subframe_.insert(pending_process->GetID());
  else
    renderer_is_subframe_.erase(pending_process->GetID());
}
void ElectronBrowserClient::AppendExtraCommandLineSwitches(
    base::CommandLine* command_line,
    int process_id) {
  
  {
    base::ThreadRestrictions::ScopedAllowIO allow_io;
    base::FilePath child_path;
    base::FilePath program =