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
}
  // This dance with `base::Owned` is to ensure that the interface stays alive
  // until the callback is called. Otherwise it would be closed at the end of
  // this function.
  auto electron_renderer =
      std::make_unique<mojo::AssociatedRemote<mojom::ElectronRenderer>>();
  frame_host->GetRemoteAssociatedInterfaces()->GetInterface(
      electron_renderer.get());
  auto* raw_ptr = electron_renderer.get();
  (*raw_ptr)->TakeHeapSnapshot(
      mojo::WrapPlatformFile(file.TakePlatformFile()),
      base::BindOnce(
          [](mojo::AssociatedRemote<mojom::ElectronRenderer>* ep,
             gin_helper::Promise<void> promise, bool success) {
            if (success) {
              promise.Resolve();
            } else {
              promise.RejectWithErrorMessage("takeHeapSnapshot failed");
            }
          },
          base::Owned(std::move(electron_renderer)), std::move(promise)));
  return handle;
}
// static
void Ws::BuildPrototype(v8::Isolate* isolate,
                                 v8::Local<v8::FunctionTemplate> prototype) {
  prototype->SetClassName(gin::StringToV8(isolate, "Ws"));
  gin_helper::Destroyable::MakeDestroyable(isolate, prototype);
  gin_helper::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
      .SetMethod("setBackgroundThrottling",