* 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
web_contents()->GetRenderViewHost()->GetWidget()->Focus();
}
void BrowserWindow::BlurWebView() {
  web_contents()->GetRenderViewHost()->GetWidget()->Blur();
}
bool BrowserWindow::IsWebViewFocused() {
  auto* host_view = web_contents()->GetRenderViewHost()->GetWidget()->GetView();
  return host_view && host_view->HasFocus();
}
v8::Local<v8::Value> BrowserWindow::GetWebContents(v8::Isolate* isolate) {
  if (web_contents_.IsEmpty())
    return v8::Null(isolate);
  return v8::Local<v8::Value>::New(isolate, web_contents_);
}
std::unique_ptr<SkRegion> BrowserWindow::DraggableRegionsToSkRegion(
    const std::vector<DraggableRegion>& regions) {
  auto sk_region = std::make_unique<SkRegion>();
  for (const DraggableRegion& region : regions) {
    sk_region->op(
        region.bounds.x(), region.bounds.y(), region.bounds.right(),
        region.bounds.bottom(),
        region.draggable ? SkRegion::kUnion_Op : SkRegion::kDifference_Op);
  }
  return sk_region;
}
void BrowserWindow::ScheduleUnresponsiveEvent(int ms) {