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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
content::Ws* source,
    const content::OpenURLParams& params) {
  if (params.disposition != WindowOpenDisposition::CURRENT_TAB) {
    Emit("-new-window", params.url, "", params.disposition, "", params.referrer,
         params.post_data);
    return nullptr;
  }
  
  if (Emit("will-navigate", params.url))
    return nullptr;
  
  
  if (IsDestroyed())
    return nullptr;
  return CommonWsDelegate::OpenURLFromTab(source, params);
}
void Ws::BeforeUnloadFired(content::Ws* tab,
                                    bool proceed,
                                    bool* proceed_to_fire_unload) {
  if (type_ == Type::BROWSER_WINDOW || type_ == Type::OFF_SCREEN)
    *proceed_to_fire_unload = proceed;
  else
    *proceed_to_fire_unload = true;
  
  Emit("before-unload-fired", proceed);
}
void Ws::SetContentsBounds(content::Ws* source,