webkit -> GraphicsContext [FillRect, DrawString, etc]-> Backend View [writes pixels]-> Backing store bitmap
                                                            |                                |
                                                            v                                |
                                                            [Invalidate]                     |
                                                            |                                |
                                                            v                                v
BWindow [resize, other window over, etc] -> [Invalidate] ->Frontend view -> [Draw()] -> [DrawBitmap]