
### 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
#if defined(OS_WIN)
  gfx::Point pos = GetPosition();
  gfx::Size size = GetSize();
  ::SetWindowPos(GetAcceleratedWidget(), HWND_TOP, pos.x(), pos.y(),
                 size.width(), size.height(),
                 SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE | SWP_SHOWWINDOW);
#elif defined(USE_X11)
  electron::MoveWindowToForeground(GetAcceleratedWidget());
#endif
}
bool NativeWindowViews::IsResizable() {
#if defined(OS_WIN)
  if (has_frame())
    return ::GetWindowLong(GetAcceleratedWidget(), GWL_STYLE) & WS_THICKFRAME;
#endif
  return CanResize();
}
void NativeWindowViews::SetAspectRatio(double aspect_ratio,