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### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [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
Browser::Get()->WillFinishLaunching();
  Browser::Get()->DidFinishLaunching(base::DictionaryValue());
#endif
  
  Browser::Get()->PreMainMessageLoopRun();
}
bool AtomBrowserMainParts::MainMessageLoopRun(int* result_code) {
  js_env_->OnMessageLoopCreated();
  exit_code_ = result_code;
  return content::BrowserMainParts::MainMessageLoopRun(result_code);
}
void AtomBrowserMainParts::PreDefaultMainMessageLoopRun(
    base::OnceClosure quit_closure) {
  Browser::Get()->SetMainMessageLoopQuitClosure(std::move(quit_closure));
}
void AtomBrowserMainParts::PostMainMessageLoopStart() {
#if defined(USE_X11)
  
  
  
  ui::SetX11ErrorHandlers(BrowserX11ErrorHandler, BrowserX11IOErrorHandler);
#endif
#if defined(OS_LINUX)
  bluez::DBusBluezManagerWrapperLinux::Initialize();
#endif
#if defined(OS_POSIX)
  HandleShutdownSignals();
#endif
}
void AtomBrowserMainParts::PostMainMessageLoopRun() {