Electron Version: 7.1.1
Operating System: Windows 10 (1803)

If I set the 'margins' option when call webContents.print method,
The app will crash with no error message.

```js
let { remote } = require("electron");
let webContents = remote.getCurrentWebContents();
webContents.print(
  {
    margins: {
      marginType: "custom",
      top: 30,
      bottom: 0,
      left: 0,
      right: 0
    }
  },
  (success, errorType) => {
    if (!success) console.log(errorType);
  }
);
```

shell/browser/api/electron_api_web_contents.cc
return type_ == Type::WEB_VIEW;
}
void Ws::AttachToIframe(content::Ws* embedder_ontents,
                                 int embedder_frame_id) {
  if (guest_delegate_)
    guest_delegate_->AttachToIframe(embedder_ontents, embedder_frame_id);
}
bool Ws::IsOffScreen() const {
#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 {