* Electron Version: 3.0.0-beta1
* Operating System (Platform and Version): macOS
* Last known working Electron version: 2.0.2

**Expected Behavior**
```css
html, body, * {
    -webkit-app-region: drag;
    -webkit-user-select: none;
    cursor: default;
}
```
should allow users to move the position of the window by dragging it directly.

**Actual behavior**
The window is not draggable.
The `cursor` and `-webkit-user-select` properties work well.

**To Reproduce**
copy the CSS above, paste it into a frameless app's `<style>` tag, and run the app.

**Screenshots**

**Additional Information**

atom/browser/api/atom_api_browser_window.cc
base::DictionaryValue web_preferences_dict;
    if (mate::ConvertFromV8(isolate, web_preferences.GetHandle(),
                            &web_preferences_dict)) {
      existing_preferences->dict()->Clear();
      existing_preferences->Merge(web_preferences_dict);
    }
  } else {
    
    web_contents = WebContents::Create(isolate, web_preferences);
  }
  web_contents_.Reset(isolate, web_contents.ToV8());
  api_web_contents_ = web_contents.get();
  api_web_contents_->AddObserver(this);
  Observe(api_web_contents_->web_contents());
  
  mate::Dictionary(isolate, web_contents->GetWrapper())
      .Set("browserWindowOptions", options);
  
  
  ui::GpuSwitchingManager::SetTransparent(window()->transparent());
  
  web_contents->SetOwnerWindow(window());
  auto* host = web_contents->web_contents()->GetRenderViewHost();
  if (host)
    host->GetWidget()->AddInputEventObserver(this);
  InitWith(isolate, wrapper);
  
  window()->InitFromOptions(options);
}
BrowserWindow::~BrowserWindow() {