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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
const GURL& validated_url) {
  bool is_main_frame = !render_frame_host->GetParent();
  int frame_process_id = render_frame_host->GetProcess()->GetID();
  int frame_routing_id = render_frame_host->GetRoutingID();
  auto weak_this = GetWeakPtr();
  Emit("did-frame-finish-load", is_main_frame, frame_process_id,
       frame_routing_id);
   ⚠️WARNING!⚠️
   Emit() triggers JS which can call destroy() on |this|. It's not safe to
   assume that |this| points to valid memory at this point.
  if (is_main_frame && weak_this)
    Emit("did-finish-load");
}
void Ws::DidFailLoad(content::RenderFrameHost* render_frame_host,
                              const GURL& url,
                              int error_code) {
  bool is_main_frame = !render_frame_host->GetParent();
  int frame_process_id = render_frame_host->GetProcess()->GetID();
  int frame_routing_id = render_frame_host->GetRoutingID();
  Emit("did-fail-load", error_code, "", url, is_main_frame, frame_process_id,
       frame_routing_id);
}
void Ws::DidStartLoading() {
  Emit("did-start-loading");
}
void Ws::DidStopLoading() {