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
}
void Ws::GoForward() {
  electron::ElectronBrowserClient::SuppressRendererProcessRestartForOnce();
  ontents()->GetController().GoForward();
}
void Ws::GoToOffset(int offset) {
  electron::ElectronBrowserClient::SuppressRendererProcessRestartForOnce();
  ontents()->GetController().GoToOffset(offset);
}
const std::string Ws::GetWebRTCIPHandlingPolicy() const {
  return ontents()->GetMutableRendererPrefs()->webrtc_ip_handling_policy;
}
void Ws::SetWebRTCIPHandlingPolicy(
    const std::string& webrtc_ip_handling_policy) {
  if (GetWebRTCIPHandlingPolicy() == webrtc_ip_handling_policy)
    return;
  ontents()->GetMutableRendererPrefs()->webrtc_ip_handling_policy =
      webrtc_ip_handling_policy;
  ontents()->SyncRendererPrefs();
}
bool Ws::IsCrashed() const {
  return ontents()->IsCrashed();
}
void Ws::SetUserAgent(const std::string& user_agent,
                               gin_helper::Arguments* args) {
  ontents()->SetUserAgentOverride(user_agent, false);
}
std::string Ws::GetUserAgent() {
  return ontents()->GetUserAgentOverride();
}