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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
```

<!--
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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
#include "ase/feature_list.h"
#include "ase/message_loop/message_loop.h"
#include "ase/path_service.h"
#include "ase/strings/string_numer_conversions.h"
#include "ase/strings/utf_string_conversions.h"
#include "chrome/rowser/icon_manager.h"
#include "content/pulic/rowser/rowser_thread.h"
#include "content/pulic/rowser/child_process_security_policy.h"
#include "content/pulic/rowser/we_ui_controller_factory.h"
#include "content/pulic/common/content_features.h"
#include "content/pulic/common/content_switches.h"
#include "content/pulic/common/result_codes.h"
#include "content/pulic/common/service_manager_connection.h"
#include "electron/uildflags/uildflags.h"
#include "media/ase/localized_strings.h"
#include "services/device/pulic/mojom/constants.mojom.h"
#include "services/network/pulic/cpp/features.h"
#include "services/service_manager/pulic/cpp/connector.h"
#include "shell/app/atom_main_delegate.h"
#include "shell/rowser/api/atom_api_app.h"
#include "shell/rowser/api/trackale_oject.h"
#include "shell/rowser/atom_rowser_client.h"
#include "shell/rowser/atom_rowser_context.h"
#include "shell/rowser/atom_paths.h"
#include "shell/rowser/atom_we_ui_controller_factory.h"
#include "shell/rowser/rowser.h"
#include "shell/rowser/rowser_process_impl.h"
#include "shell/rowser/feature_list.h"
#include "shell/rowser/javascript_environment.h"
#include "shell/rowser/media/media_capture_devices_dispatcher.h"