* 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/native_window_mac.h
void Show() override;
  void ShowInactive() override;
  void Hide() override;
  bool IsVisible() override;
  bool IsEnabled() override;
  void SetEnabled(bool enable) override;
  void Maximize() override;
  void Unmaximize() override;
  bool IsMaximized() override;
  void Minimize() override;
  void Restore() override;
  bool IsMinimized() override;
  void SetFullScreen(bool fullscreen) override;
  bool IsFullscreen() const override;
  void SetBounds(const gfx::Rect& bounds, bool animate = false) override;
  gfx::Rect GetBounds() override;
  void SetContentSizeConstraints(
      const extensions::SizeConstraints& size_constraints) override;
  void SetResizable(bool resizable) override;
  void MoveTop() override;
  bool IsResizable() override;
  void SetMovable(bool movable) override;
  void SetAspectRatio(double aspect_ratio,
                      const gfx::Size& extra_size) override;
  void PreviewFile(const std::string& path,
                   const std::string& display_name) override;
  void CloseFilePreview() override;
  bool IsMovable() override;
  void SetMinimizable(bool minimizable) override;
  bool IsMinimizable() override;