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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:**
  * 5.0.0
* **Operating System:**
  * macOS 10.14.4
* **Last Known Working Electron version:**:
  * 4.1.4

### Expected Behavior
Quitting while a debugger is attached to the process results in the application exiting without error.

### Actual Behavior
Qutting while a debugger is still attached results in the application crashing and macOS showing its crash report dialog.

### To Reproduce

1. Run electron with `--inspect=9229` or `--inspect-brk=9229`.
2. Attach with a debugger (such as Visual Studio Code).
3. Quit electron without detaching.

Below is a repo that reproduces the issue:
[Repo that reproduces the issue](https://github.com/kpes/electron5attachquitcrash)

```sh
$ git clone https://github.com/kpes/electron5attachquitcrash.git
$ npm install
```

atom/browser/atom_browser_main_parts.cc
node_bindings_->PrepareMessageLoop();
  node_bindings_->RunMessageLoop();
  
  url::LockSchemeRegistries();
#if defined(USE_X11)
  ui::TouchFactory::SetTouchDeviceListFromCommandLine();
#endif
  
  gc_timer_.Start(FROM_HERE, base::TimeDelta::FromMinutes(1),
                  base::Bind(&v8::Isolate::LowMemoryNotification,
                             base::Unretained(js_env_->isolate())));
  content::WebUIControllerFactory::RegisterFactory(
      AtomWebUIControllerFactory::GetInstance());
  
  auto* command_line = base::CommandLine::ForCurrentProcess();
  if (command_line->HasSwitch(switches::kRemoteDebuggingPort))
    DevToolsManagerDelegate::StartHttpHandler();
#if defined(USE_X11)
  libgtkui::GtkInitFromCommandLine(*base::CommandLine::ForCurrentProcess());
#endif
#if !defined(OS_MACOSX)