* Electron version: 2.0.0-beta.7
* Operating system: macOS 10.13.4

### Expected behavior

<!-- What do you think should happen? -->
When HTML fullscreen mode is active, exiting fullscreen on the window level (clicking the green button or calling `win.setFullScreen(false)` should also exit HTML fullscreen mode.

### Actual behavior

HTML fullscreen mode stays active. Chrome correctly exits HTML fullscreen mode.

### How to reproduce

Use console in the default_app:

```
document.addEventListener('webkitfullscreenchange', () => console.log('webkitfullscreenchange'));
document.documentElement.webkitRequestFullscreen();
```

now exit fullscreen by clicking the green button or run `require('electron').remote.getCurrentWindow().setFullScreen(false);`

Compare to what happens when you do the same in Chrome/Chromium
`webkitfullscreenchange` should be logged twice (once for enter, once for exit)
`document.webkitFullscreenElement` should also be `null`

Possible workaround is:
```
win.on('leave-full-screen', () => {
  win.webContents.executeJavaScript('document.webkitExitFullscreen();');
});
```

atom/browser/api/atom_api_browser_window.h
void OnInputEvent(const blink::WebInputEvent& event) override;
  
  void RenderViewHostChanged(content::RenderViewHost* old_host,
                             content::RenderViewHost* new_host) override;
  void RenderViewCreated(content::RenderViewHost* render_view_host) override;
  void DidFirstVisuallyNonEmptyPaint() override;
  void BeforeUnloadDialogCancelled() override;
  void OnRendererUnresponsive(content::RenderWidgetHost*) override;
  bool OnMessageReceived(const IPC::Message& message,
                         content::RenderFrameHost* rfh) override;
  
  void OnCloseContents() override;
  void OnRendererResponsive() override;
  
  void RequestPreferredWidth(int* width) override;
  void OnCloseButtonClicked(bool* prevent_default) override;
  
  void OnWindowClosed() override;
  void OnWindowBlur() override;
  void OnWindowFocus() override;
  void OnWindowResize() override;
  void Focus() override;
  void Blur() override;
  void SetBackgroundColor(const std::string& color_name) override;
  void SetBrowserView(v8::Local<v8::Value> value) override;
  void SetVibrancy(mate::Arguments* args) override;
  
  void FocusOnWebView();
  void BlurWebView();
  bool IsWebViewFocused();