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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
prefs.sandbox = web_preferences->IsEnabled(options::kSandbox);
    prefs.native_window_open =
        web_preferences->IsEnabled(options::kNativeWindowOpen);
    prefs.disable_popups = web_preferences->IsEnabled("disablePopups");
    prefs.web_security = web_preferences->IsEnabled(options::kWebSecurity,
                                                    true );
    prefs.browser_context = host->GetBrowserContext();
  }
  AddProcessPreferences(host->GetID(), prefs);
  
  host->AddObserver(this);
}
content::SpeechRecognitionManagerDelegate*
ElectronBrowserClient::CreateSpeechRecognitionManagerDelegate() {
  return new ElectronSpeechRecognitionManagerDelegate;
}
content::TtsPlatform* ElectronBrowserClient::GetTtsPlatform() {
  return nullptr;
}
void ElectronBrowserClient::OverrideWebkitPrefs(
    content::RenderViewHost* host,
    content::WebPreferences* prefs) {
  prefs->javascript_enabled = true;
  prefs->web_security_enabled = true;
  prefs->plugins_enabled = true;
  prefs->dom_paste_enabled = true;
  prefs->allow_scripts_to_close_windows = true;
  prefs->javascript_can_access_clipboard = true;
  prefs->local_storage_enabled = true;
  prefs->databases_enabled = true;