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### Issue Details
App crashes when call `webContents.print()`
* **Electron Version:**
8.0.2
* **Operating System:**
Mac OS Catalina 10.15.3 (19D76)
* **Last Known Working Electron version:**
Electron 6 did not crash when print but has other bugs with printing

### Expected Behavior
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App should not crash
### Actual Behavior
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App crashes
### To Reproduce
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Can be reproduced with this Fiddle
https://gist.github.com/1aced5931b191c07adb6a111f937a4e1

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### Screenshots
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### Additional Information
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shell/browser/api/electron_api_web_contents.cc
void Ws::OnGetDefaultPrinter(
    base::Value print_settings,
    printing::CompletionCallback print_callback,
    base::string16 device_name,
    bool silent,
    base::string16 default_printer) {
  // The content::Ws might be already deleted at this point, and the
  // PrintViewManagerBasic class does not do null check.
  if (!ontents()) {
    if (print_callback)
      std::move(print_callback).Run(false, "failed");
    return;
  }
  base::string16 printer_name =
      device_name.empty() ? default_printer : device_name;
  print_settings.SetStringKey(printing::kSettingDeviceName, printer_name);
  auto* print_view_manager =
      printing::PrintViewManagerBasic::FromWs(ontents());
  auto* focused_frame = ontents()->GetFocusedFrame();
  auto* rfh = focused_frame && focused_frame->HasSelection()
                  ? focused_frame
                  : ontents()->GetMainFrame();
  print_view_manager->PrintNow(rfh, silent, std::move(print_settings),
                               std::move(print_callback));
}
void Ws::Print(gin_helper::Arguments* args) {
  gin_helper::Dictionary options =
      gin::Dictionary::CreateEmpty(args->isolate());
  base::Value settings(base::Value::Type::DICTIONARY);
  if (args->Length() >= 1 && !args->GetNext(&options)) {