Class used to implement content for a popup window.
See Also: PopupWindow with full example.
| editorWindow | The EditorWindow that contains the popup content. | 
| GetWindowSize | The size of the popup window. | 
| OnClose | Callback when the popup window is closed. | 
| OnGUI | Callback for drawing GUI controls for the popup window. | 
| OnOpen | Callback when the popup window is opened. |