
### Preflight Checklist
* [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:**
  * 6.1.5
* **Operating System:**
  * Windows 10
* **Last Known Working Electron version:**
  * ?

### Expected Behavior
If the window is focusable then the focus event should be triggered

### Actual Behavior
Setting the window initially to focusable: false and later to true again will not enable the focus events. Even when focusing the window, the event will never be triggered.

### To Reproduce
```
let browserWindow1 = new BrowserWindow({
	show: false,
	x: 1,
	y: 1,
	width: 800,
	height: 700,
	title: "test-title-1",
	focusable: false,
});
browserWindow1.on("focus", () => {console.log("focus");});
browserWindow1.loadURL("http://www.google.com");
browserWindow1.setFocusable(true);
browserWindow1.show();
```

shell/browser/native_window_views.cc
options.Get(options::kType, &window_type);
#if defined(USE_X11)
  
  window_state_watcher_ = std::make_unique<WindowStateWatcher>(this);
  
  bool use_dark_theme = false;
  if (options.Get(options::kDarkTheme, &use_dark_theme) && use_dark_theme) {
    SetGTKDarkThemeEnabled(use_dark_theme);
  }
  
  
  std::vector<::Atom> state_atom_list;
  bool skip_taskbar = false;
  if (options.Get(options::kSkipTaskbar, &skip_taskbar) && skip_taskbar) {
    state_atom_list.push_back(GetAtom("_NET_WM_STATE_SKIP_TASKBAR"));
  }
  
  if (fullscreen) {
    state_atom_list.push_back(GetAtom("_NET_WM_STATE_FULLSCREEN"));
  }
  if (parent) {
    SetParentWindow(parent);
    
    window_type = "dialog";
    
    if (is_modal())
      state_atom_list.push_back(GetAtom("_NET_WM_STATE_MODAL"));
  }
  if (!state_atom_list.empty())
    ui::SetAtomArrayProperty(GetAcceleratedWidget(), "_NET_WM_STATE", "ATOM",