update-save-button in drscheme:unit:frame
(-> voidsenda-drscheme:unit:frameupdate-save-buttonmodified?)
modified?: booleanThis method hides or shows the save button, based on the
modified?argument.If the save button has not been created yet, it remembers the
modified?argument as an initial visibility for the save button.This method is called by the
set-modifiedmethod.