### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [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.

Ref #19447

### Issue Details

* **Electron Version:**
  * 9.0.0-beta.24
* **Operating System:**
  * macOS 10.15, Windows 10
* **Last Known Working Electron version:**
  * none

### Expected Behavior
`e.sender` object received from an extension background page should have `webPreferences` and `session` initialized. It looks like `options` in `api::WebContents` constructor don't get initialized properly for an extension background page.

### Actual Behavior
`e.sender` object doesn't have `session` and `e.sender.getWebPreferences()` returns `null`.

### To Reproduce
https://github.com/sentialx/electron-quick-start/tree/extensions/no-session

Just run it and you will see something like this:
![image](https://user-images.githubusercontent.com/11065386/82097607-82994400-9703-11ea-8291-0eb987d8aca0.png)

### Additional Information
This is a real blocker for anyone who would want to provide own `chrome` APIs in background pages initialized from different sessions.
shell/browser/api/electron_api_web_contents.cc
std::string accept_languages =
      g_browser_process->GetApplicationLocale() + ",";
  for (auto const& language : electron::GetPreferredLanguages()) {
    if (language == g_browser_process->GetApplicationLocale())
      continue;
    accept_languages += language + ",";
  }
  accept_languages.pop_back();
  prefs->accept_languages = accept_languages;
#if defined(OS_LINUX) || defined(OS_WIN)
  
  static const base::NoDestructor<gfx::FontRenderParams> params(
      gfx::GetFontRenderParams(gfx::FontRenderParamsQuery(), nullptr));
  prefs->should_antialias_text = params->antialiasing;
  prefs->use_subpixel_positioning = params->subpixel_positioning;
  prefs->hinting = params->hinting;
  prefs->use_autohinter = params->autohinter;
  prefs->use_bitmaps = params->use_bitmaps;
  prefs->subpixel_rendering = params->subpixel_rendering;
#endif
  
  if (auto interval = GetCursorBlinkInterval())
    prefs->caret_blink_interval = *interval;
  
  new WsPreferences(ontents(), options);
  WsPermissionHelper::CreateForWs(ontents());
  SecurityStateTabHelper::CreateForWs(ontents());