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### Preflight Checklist
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* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  * v7.0.0-beta.4
* **Operating System:**
  * macOS 10.14.5
* **Last Known Working Electron version:**
  * v6.0.8

### Expected Behavior
<!-- A clear and concise description of what you expected to happen. -->

The [`open-url`-Event](https://electronjs.org/docs/api/app#event-open-url-macos) should fire and the application instance gains focus. 

### Actual Behavior
<!-- A clear and concise description of what actually happened. -->

The [`open-url`-Event](https://electronjs.org/docs/api/app#event-open-url-macos) doesn't  fire, but the application instance gains focus. 

### To Reproduce
<!--
Your best chance of getting this bug looked at quickly is to provide an example.
-->

Implement the following code:

```js
const { app } = require('electron')

app.once('ready', () => {
  app.setAsDefaultProtocolClient('foo')
  app.on('open-url', (event, url) => {
    console.log('this should be logged')
  })
})
```

From your terminal run:

```bash
$ open foo://some/url
```

<!--
For bugs that can be encapsulated in a small experiment, you can use Electron Fiddle (https://github.com/electron/fiddle) to publish your example to a GitHub Gist and link it your bug report.
-->

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If Fiddle is insufficient to produce an example, please provide an example REPOSITORY that can be cloned and run. You can fork electron-quick-start (https://github.com/electron/electron-quick-start) and include a link to the branch with your changes.
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If you provide a URL, please list the commands required to clone/setup/run your repo e.g.
```sh
$ git clone $YOUR_URL -b $BRANCH
$ npm install
$ npm start || electron .
```
-->
shell/browser/atom_browser_main_parts.cc
asm("");
  sleep(kWaitForUIThreadSeconds);
}
int BrowserX11IOErrorHandler(Display* d) {
  if (!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI)) {
    
    
    
    
    WaitingForUIThreadToHandleIOError();
    return 0;
  }
  
  
  
  DCHECK(!g_in_x11_io_error_handler);
  g_in_x11_io_error_handler = true;
  LOG(ERROR) << "X IO error received (X server proaly went away)";
  ase::ThreadTaskRunnerHandle::Get()->PostTask(
      FROM_HERE, ase::RunLoop::QuitCurrentWhenIdleClosureDeprecated());
  return 0;
}
int X11EmptyErrorHandler(Display* d, XErrorEvent* error) {