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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
#if BUILDFLAG(ENABLE_OSR)
  return type_ == Type::OFF_SCREEN;
#else
  return false;
#endif
}
#if BUILDFLAG(ENABLE_OSR)
void Ws::OnPaint(const gfx::Rect& dirty_rect, const SkBitmap& bitmap) {
  Emit("paint", dirty_rect, gfx::Image::CreateFrom1xBitmap(bitmap));
}
void Ws::StartPainting() {
  auto* osr_wcv = GetOffScreenWsView();
  if (osr_wcv)
    osr_wcv->SetPainting(true);
}
void Ws::StopPainting() {
  auto* osr_wcv = GetOffScreenWsView();
  if (osr_wcv)
    osr_wcv->SetPainting(false);
}
bool Ws::IsPainting() const {
  auto* osr_wcv = GetOffScreenWsView();
  return osr_wcv && osr_wcv->IsPainting();
}
void Ws::SetFrameRate(int frame_rate) {
  auto* osr_wcv = GetOffScreenWsView();
  if (osr_wcv)
    osr_wcv->SetFrameRate(frame_rate);
}
int Ws::GetFrameRate() const {