
### 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
params.ownership = views::Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
  params.bounds = bounds;
  params.delegate = this;
  params.type = views::Widget::InitParams::TYPE_WINDOW;
  params.remove_standard_frame = !has_frame();
  if (transparent())
    params.opacity = views::Widget::InitParams::WindowOpacity::kTranslucent;
  
  
  if (transparent() && !has_frame())
    params.shadow_type = views::Widget::InitParams::ShadowType::kNone;
  bool focusable;
  if (options.Get(options::kFocusable, &focusable) && !focusable)
    params.activatable = views::Widget::InitParams::ACTIVATABLE_NO;
#if defined(OS_WIN)
  if (parent)
    params.parent = parent->GetNativeWindow();
  params.native_widget = new AtomDesktopNativeWidgetAura(this);
#elif defined(USE_X11)
  std::string name = Browser::Get()->GetName();
  
  params.wm_role_name = "browser-window";
  
  params.wm_class_name = base::ToLowerASCII(name);
  params.wm_class_class = name;
#endif
  widget()->Init(std::move(params));
  bool fullscreen = false;
  options.Get(options::kFullscreen, &fullscreen);
  std::string window_type;