**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
frame->GetRoutingID(), frame->GetLastCommittedOrigin(), browser_context,
      &next_id_);
}
bool ElectronBrowserClient::WillCreateURLLoaderFactory(
    content::BrowserContext* browser_context,
    content::RenderFrameHost* frame_host,
    int render_process_id,
    URLLoaderFactoryType type,
    const url::Origin& request_initiator,
    absl::optional<int64_t> navigation_id,
    ukm::SourceIdObj ukm_source_id,
    mojo::PendingReceiver<network::mojom::URLLoaderFactory>* factory_receiver,
    mojo::PendingRemote<network::mojom::TrustedURLLoaderHeaderClient>*
        header_client,
    bool* bypass_redirect_checks,
    bool* disable_secure_dns,
    network::mojom::URLLoaderFactoryOverridePtr* factory_override) {
  v8::Isolate* isolate = JavascriptEnvironment::GetIsolate();
  v8::HandleScope scope(isolate);
  auto web_request = api::WebRequest::FromOrCreate(isolate, browser_context);
  DCHECK(web_request.get());
#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
  if (!web_request->HasListener()) {
    auto* web_request_api = extensions::BrowserContextKeyedAPIFactory<
        extensions::WebRequestAPI>::Get(browser_context);
    DCHECK(web_request_api);
    bool use_proxy_for_web_request =
        web_request_api->MaybeProxyURLLoaderFactory(
            browser_context, frame_host, render_process_id, type, navigation_id,
            ukm_source_id, factory_receiver, header_client);