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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
}
int Ws::GetProcessID() const {
  return ontents()->GetMainFrame()->GetProcess()->GetID();
}
base::ProcessId Ws::GetOSProcessID() const {
  base::ProcessHandle process_handle =
      ontents()->GetMainFrame()->GetProcess()->GetProcess().Handle();
  return base::GetProcId(process_handle);
}
base::ProcessId Ws::GetOSProcessIdForFrame(
    const std::string& name,
    const std::string& document_url) const {
  for (auto* frame : ontents()->GetAllFrames()) {
    if (frame->GetFrameName() == name &&
        frame->GetLastCommittedURL().spec() == document_url) {
      return base::GetProcId(frame->GetProcess()->GetProcess().Handle());
    }
  }
  return base::kNullProcessId;
}
Ws::Type Ws::GetType() const {
  return type_;
}
bool Ws::Equal(const Ws* ontents) const {
  return ID() == ontents->ID();
}
void Ws::LoadURL(const GURL& url,
                          const gin_helper::Dictionary& options) {
  if (!url.is_valid() || url.spec().size() > url::kMaxURLChars) {
    Emit("did-fail-load", static_cast<int>(net::ERR_INVALID_URL),