
### 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
#include "shell/browser/native_window_views.h"
#if defined(OS_WIN)
#include <wrl/client.h>
#endif
#include <memory>
#include <tuple>
#include <utility>
#include <vector>
#include "base/numerics/ranges.h"
#include "base/stl_util.h"
#include "base/strings/utf_string_conversions.h"
#include "content/public/browser/browser_thread.h"
#include "content/public/browser/desktop_media_id.h"
#include "shell/browser/api/atom_api_web_contents.h"
#include "shell/browser/native_browser_view_views.h"
#include "shell/browser/ui/inspectable_web_contents.h"
#include "shell/browser/ui/inspectable_web_contents_view.h"
#include "shell/browser/ui/views/root_view.h"
#include "shell/browser/web_contents_preferences.h"
#include "shell/browser/web_view_manager.h"
#include "shell/browser/window_list.h"
#include "shell/common/atom_constants.h"
#include "shell/common/gin_converters/image_converter.h"
#include "shell/common/gin_helper/dictionary.h"
#include "shell/common/options_switches.h"
#include "ui/aura/window_tree_host.h"
#include "ui/base/hit_test.h"
#include "ui/gfx/image/image.h"