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### Preflight Checklist
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* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**  9.0.0
  <!-- (output of `node_modules/.bin/electron --version`) e.g. 4.0.3 -->
* **Operating System:** Windows 10 (1904)
  <!-- (Platform and Version) e.g. macOS 10.13.6 / Windows 10 (1803) / Ubuntu 18.04 x64 -->
* **Last Known Working Electron version:** 8.2.0
  <!-- (if applicable) e.g. 3.1.0 -->

### Expected Behavior
<!-- A clear and concise description of what you expected to happen. -->
Setting BrowserWindow webPreferences: { webSecurity: false } should disable the CORS policy

### Actual Behavior
<!-- A clear and concise description of what actually happened. -->
Although I am receiving the electron security warnings for "Disabled webSecurity","allowRunningInsecureContent" and "Insecure Content-Security-Policy" in the console I am still getting COR policy errors on my requests.

**Here is an example:**

Access to XMLHttpRequest at 'http://localhost:8080/users/login' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.

shell/browser/electron_browser_client.cc
base::FilePath user_data_dir;
  base::PathService::Get(DIR_USER_DATA, &user_data_dir);
  DCHECK(!user_data_dir.empty());
  return user_data_dir.Append(FILE_PATH_LITERAL("FontLookupTableCache"));
}
bool ElectronBrowserClient::ShouldEnableStrictSiteIsolation() {
  
  return true;
}
void ElectronBrowserClient::BindHostReceiverForRenderer(
    content::RenderProcessHost* render_process_host,
    mojo::GenericPendingReceiver receiver) {
#if BUILDFLAG(ENABLE_BUILTIN_SPELLCHECKER)
  if (auto host_receiver = receiver.As<spellcheck::mojom::SpellCheckHost>()) {
    SpellCheckHostChromeImpl::Create(render_process_host->GetID(),
                                     std::move(host_receiver));
    return;
  }
#endif
}
void BindBadgeManagerFrameReceiver(
    content::RenderFrameHost* frame,
    mojo::PendingReceiver<blink::mojom::BadgeService> receiver) {
  LOG(WARNING) << "The Chromium Badging API is not available in Electron";
}
#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
void BindMimeHandlerService(