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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
// be destroyed on close, and WsDestroyed would be called for it, so
// we need to make sure the api::Ws is also deleted.
// For #4, the Ws will be destroyed by embedder.
void Ws::WsDestroyed() {
  // Cleanup relationships with other parts.
  RemoveFromWeakMap();
  // We can not call Destroy here because we need to call Emit first, but we
  // also do not want any method to be used, so just mark as destroyed here.
  MarkDestroyed();
  Emit("destroyed");
  // For guest view based on OOPIF, the Ws is released by the embedder
  // frame, and we need to clear the reference to the memory.
  if (IsGuest() && managed_ontents()) {
    managed_ontents()->ReleaseWs();
    ResetManagedWs(false);
  }
  // Destroy the native class in next tick.
  base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE, GetDestroyClosure());
}
void Ws::NavigationEntryCommitted(
    const content::LoadCommittedDetails& details) {
  Emit("navigation-entry-committed", details.entry->GetURL(),
       details.is_same_document, details.did_replace_entry);
}
void Ws::SetBackgroundThrottling(bool allowed) {
  background_throttling_ = allowed;
  auto* rfh = ontents()->GetMainFrame();
  if (!rfh)
    return;
  auto* rwhv = rfh->GetView();