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### Issue Details

* **Electron Version:** v7 nightly 20190615
* **Operating System:** Windows 10 (1809)
* **Last Known Working Electron version:** v7 nightly 20190613

### Expected Behavior
Icon is shown in message box according to the `type` property.

### Actual Behavior
Icon is not shown.

### To Reproduce
```
const { app, dialog } = require("electron")
app.on("ready", () => {
  dialog.showMessageBox({
    title: "Also, something with windows looks broken.",
    type: "info"
  })
})
```

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### Screenshots
_before_
![image](https://user-images.githubusercontent.com/8472721/61568972-1cd42100-aa3a-11e9-9fa6-6f4792eef625.png)

_after_
![image](https://user-images.githubusercontent.com/8472721/61569000-2cec0080-aa3a-11e9-9805-bb9900320f1d.png)


### Additional Information
I'm pretty sure this issue was introduced by https://github.com/electron/electron/pull/18732. Any ideas @codebytere? Probs the `icon` property is broken as well.
shell/common/native_mate_converters/message_box_converter.cc
#include "shell/common/native_mate_converters/message_box_converter.h"
#include "native_mate/dictionary.h"
#include "shell/browser/api/atom_api_browser_window.h"
#include "shell/common/native_mate_converters/file_path_converter.h"
#include "shell/common/native_mate_converters/image_converter.h"
namespace mate {
bool Converter<electron::MessageBoxSettings>::FromV8(