Little optimization in Frame rendering speed.

By explicitly specifying the size of the frame borders, computing layout
dimensions is much quicker.

Author: jonathanslenders

prompt_toolkit/widgets/base.py

@@ -529,7 +529,9 @@ def has_title() -> bool:
                         fill(width=1, height=1, char=Border.BOTTOM_LEFT),
                         fill(char=Border.HORIZONTAL),
                         fill(width=1, height=1, char=Border.BOTTOM_RIGHT),
-                    ]
+                    ],
+                    # specifying height here will increase the rendering speed.
+                    height=1,
                 ),
             ],
             width=width,