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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
v8::Local<v8::Value> message_value,
                              base::Optional<v8::Local<v8::Value>> transfer) {
  blink::TransferableMessage transferable_message;
  if (!electron::SerializeV8Value(isolate(), message_value,
                                  &transferable_message)) {
     SerializeV8Value sets an exception.
    return;
  }
  std::vector<gin::Handle<MessagePort>> wrapped_ports;
  if (transfer) {
    if (!gin::ConvertFromV8(isolate(), *transfer, &wrapped_ports)) {
      isolate()->ThrowException(v8::Exception::Error(
          gin::StringToV8(isolate(), "Invalid value for transfer")));
      return;
    }
  }
  bool threw_exception = false;
  transferable_message.ports =
      MessagePort::DisentanglePorts(isolate(), wrapped_ports, &threw_exception);
  if (threw_exception)
    return;
  content::RenderFrameHost* frame_host = ontents()->GetMainFrame();
  mojo::AssociatedRemote<mojom::ElectronRenderer> electron_renderer;
  frame_host->GetRemoteAssociatedInterfaces()->GetInterface(&electron_renderer);
  electron_renderer->ReceivePostMessage(channel,
                                        std::move(transferable_message));
}
void Ws::MessageSync(bool internal,