
### 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
return is_enabled_ && (num_modal_children_ == 0);
}
void NativeWindowViews::SetEnabledInternal(bool enable) {
  if (enable && IsEnabled()) {
    return;
  } else if (!enable && !IsEnabled()) {
    return;
  }
#if defined(OS_WIN)
  ::EnableWindow(GetAcceleratedWidget(), enable);
#elif defined(USE_X11)
  views::DesktopWindowTreeHostLinux* tree_host =
      views::DesktopWindowTreeHostLinux::GetHostForWidget(
          GetAcceleratedWidget());
  if (enable) {
    tree_host->RemoveEventRewriter(event_disabler_.get());
    event_disabler_.reset();
  } else {
    event_disabler_ = std::make_unique<EventDisabler>();
    tree_host->AddEventRewriter(event_disabler_.get());
  }
#endif
}
#if defined(USE_X11)
void NativeWindowViews::Maximize() {