**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
#include "extensions/browser/process_manager.h"
#include "extensions/browser/process_map.h"
#include "extensions/browser/url_loader_factory_manager.h"
#include "extensions/common/api/mime_handler.mojom.h"
#include "extensions/common/constants.h"
#include "extensions/common/extension.h"
#include "extensions/common/switches.h"
#include "shell/browser/extensions/electron_extension_message_filter.h"
#include "shell/browser/extensions/electron_extension_system.h"
#include "shell/browser/extensions/electron_extension_web_contents_observer.h"
#include "third_party/blink/public/common/associated_interfaces/associated_interface_registry.h"
#endif
#if BUILDFLAG(ENABLE_PLUGINS)
#include "chrome/browser/plugins/plugin_response_interceptor_url_loader_throttle.h"  
#include "shell/browser/plugins/plugin_utils.h"
#endif
#if BUILDFLAG(IS_MAC)
#include "content/common/mac_helpers.h"
#include "content/public/common/child_process_host.h"
#endif
#if BUILDFLAG(IS_LINUX) && !defined(MAS_BUILD)
#include "base/debug/leak_annotations.h"
#include "components/crash/content/browser/crash_handler_host_linux.h"
#include "components/crash/core/app/breakpad_linux.h"  
#include "components/crash/core/app/crash_switches.h"  
#include "components/crash/core/app/crashpad.h"        
#endif
#if BUILDFLAG(ENABLE_PICTURE_IN_PICTURE) && BUILDFLAG(IS_WIN)
#include "chrome/browser/ui/views/overlay/document_overlay_window_views.h"
#include "chrome/browser/ui/views/overlay/video_overlay_window_views.h"