* 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.cc
#include "atom/browser/api/atom_api_browser_window.h"
#include "atom/browser/browser.h"
#include "atom/browser/unresponsive_suppressor.h"
#include "atom/browser/web_contents_preferences.h"
#include "atom/browser/window_list.h"
#include "atom/common/api/api_messages.h"
#include "atom/common/api/constructor.h"
#include "atom/common/color_util.h"
#include "atom/common/native_mate_converters/callback.h"
#include "atom/common/native_mate_converters/value_converter.h"
#include "atom/common/options_switches.h"
#include "base/threading/thread_task_runner_handle.h"
#include "content/browser/renderer_host/render_widget_host_impl.h"
#include "content/public/browser/render_process_host.h"
#include "content/public/browser/render_view_host.h"
#include "native_mate/dictionary.h"
#include "ui/gl/gpu_switching_manager.h"
#include "atom/common/node_includes.h"
namespace atom {
namespace api {
BrowserWindow::BrowserWindow(v8::Isolate* isolate,
                             v8::Local<v8::Object> wrapper,
                             const mate::Dictionary& options)
    : TopLevelWindow(isolate, options), weak_factory_(this) {
  mate::Handle<class WebContents> web_contents;