**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
ElectronBrowserClient::CreateBrowserMainParts(
    content::MainFunctionParams params) {
  auto browser_main_parts =
      std::make_unique<ElectronBrowserMainParts>(std::move(params));
#if BUILDFLAG(IS_MAC)
  browser_main_parts_ = browser_main_parts.get();
#endif
  return browser_main_parts;
}
void ElectronBrowserClient::WebNotificationAllowed(
    content::RenderFrameHost* rfh,
    base::OnceCallback<void(bool, bool)> callback) {
  content::WebContents* web_contents =
      content::WebContents::FromRenderFrameHost(rfh);
  if (!web_contents) {
    std::move(callback).Run(false, false);
    return;
  }
  auto* permission_helper =
      WebContentsPermissionHelper::FromWebContents(web_contents);
  if (!permission_helper) {
    std::move(callback).Run(false, false);
    return;
  }
  permission_helper->RequestWebNotificationPermission(
      base::BindOnce(std::move(callback), web_contents->IsAudioMuted()));
}
void ElectronBrowserClient::RenderProcessHostDestroyed(