**Is your feature request related to a problem? Please describe.**
Notifications, Geolocation, Device motion/orientation, EME, getUserMedia, AppCache require a secure origin to work in Chromium. HTTP URLs are not considered secure.
That's why Chromium provides the command-line switch
`--unsafely-treat-insecure-origin-as-secure="$url"` to circumvent this problem.
Unfortunately it's not working in Electron.

**Describe the solution you'd like**
Please make it work. In the renderer. I'd suggest simply like 
```
new BrowserWindow({
  webPreferences: {
    additionalArguments: {
    '--unsafely-treat-insecure-origin-as-secure', 'http://insecure-origin'
    }
}
```
Or a new option `considerSecure: String[]` to `BrowserWindow.webPreferences`.
I guess it should be not too hard to implement since Chromium already supports it and it seems to get lost only in the process of Electron integration.

**Describe alternatives you've considered**
- `app.commandLine.appendSwitch('unsafely-treat-insecure-origin-as-secure', $url)` in the main thread
- Invisible [BrowserWindow](https://github.com/electron/electron/blob/master/docs/api/browser-window.md) with secure origin + IPC
- `<iframe>` on a secure origin
- localhost-Proxy
- Using Data URLs in [loadURL](https://github.com/electron/electron/blob/master/docs/api/browser-window.md#winloadurlurl-options): `data:text/html,<script>new Notification("hi")</script>`
- webFrame.registerURLSchemeAsPrivileged

**Additional context**
'Deprecating Powerful Features on Insecure Origins' https://goo.gl/rStTGz
When the flag is set in Chromium a message appears under the address bar, saying that
'You are using an unsupported command-line flag'.
![image](https://user-images.githubusercontent.com/23075755/47640947-1c6ebf80-db65-11e8-9e6e-d7a5bd90c208.png)
Nonetheless the features are then working on the origin treated securely.
shell/browser/electron_browser_client.cc
if (bypass_redirect_checks)
      *bypass_redirect_checks = use_proxy_for_web_request;
    if (use_proxy_for_web_request)
      return true;
  }
#endif
  auto proxied_receiver = std::move(*factory_receiver);
  mojo::PendingRemote<network::mojom::URLLoaderFactory> target_factory_remote;
  *factory_receiver = target_factory_remote.InitWithNewPipeAndPassReceiver();
  
  
  
  
  
  std::unique_ptr<extensions::ExtensionNavigationUIData> navigation_ui_data;
  if (navigation_id.has_value()) {
    navigation_ui_data =
        std::make_unique<extensions::ExtensionNavigationUIData>();
  }
  mojo::PendingReceiver<network::mojom::TrustedURLLoaderHeaderClient>
      header_client_receiver;
  if (header_client)
    header_client_receiver = header_client->InitWithNewPipeAndPassReceiver();
  auto* protocol_registry =
      ProtocolRegistry::FromBrowserContext(browser_context);
  new ProxyingURLLoaderFactory(
      web_request.get(), protocol_registry->intercept_handlers(),
      render_process_id,
      frame_host ? frame_host->GetRoutingID() : MSG_ROUTING_NONE,
      frame_host ? frame_host->GetRenderViewHost()->GetRoutingID()