* 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
if (!Browser::Get()->is_ready()) {
    args->ThrowError("Cannot create BrowserWindow before app is ready");
    return nullptr;
  }
  if (args->Length() > 1) {
    args->ThrowError();
    return nullptr;
  }
  mate::Dictionary options;
  if (!(args->Length() == 1 && args->GetNext(&options))) {
    options = mate::Dictionary::CreateEmpty(args->isolate());
  }
  return new BrowserWindow(args->isolate(), args->GetThis(), options);
}
void BrowserWindow::BuildPrototype(v8::Isolate* isolate,
                                   v8::Local<v8::FunctionTemplate> prototype) {
  prototype->SetClassName(mate::StringToV8(isolate, "BrowserWindow"));
  mate::ObjectTemplateBuilder(isolate, prototype->PrototypeTemplate())
      .SetMethod("focusOnWebView", &BrowserWindow::FocusOnWebView)
      .SetMethod("blurWebView", &BrowserWindow::BlurWebView)
      .SetMethod("isWebViewFocused", &BrowserWindow::IsWebViewFocused)
      .SetProperty("webContents", &BrowserWindow::GetWebContents);
}
v8::Local<v8::Value> BrowserWindow::From(v8::Isolate* isolate,