auto-resize-tool-bars

auto-resize-tool-bars is a variable defined in `C source code'.
Its value is

t

Documentation:
Non-nil means automatically resize tool-bars.
This dynamically changes the tool-bar's height to the minimum height
that is needed to make all tool-bar items visible.
If value is `grow-only', the tool-bar's height is only increased
automatically; to decrease the tool-bar height, use M-x recenter.