Introduce refresh_window method

Introduce refresh_window method

This replaces tui_refresh_win with a new refresh_window method.  This
removes another spot that was checking the window's type.

gdb/ChangeLog
2019-06-25  Tom Tromey  <tom@tromey.com>

	* tui/tui-winsource.c (tui_erase_source_content)
	(tui_show_source_content, tui_show_exec_info_content)
	(tui_erase_exec_info_content): Use refresh_window method.
	* tui/tui-wingeneral.h (tui_refresh_win): Don't declare.
	* tui/tui-wingeneral.c (tui_gen_win_info::refresh_window): Rename
	from tui_refresh_win.
	(tui_data_window::refresh_window): New method.
	(tui_win_info::refresh, tui_source_window_base::refresh)
	(tui_refresh_all): Use refresh_window method.
	* tui/tui-stack.c (tui_show_locator_content): Call refresh_window
	method.
	* tui/tui-regs.c (tui_display_register): Call refresh_window
	method.
	* tui/tui-layout.c (show_source_disasm_command)
	(show_source_or_disasm_and_command): Call refresh_window method.
	* tui/tui-data.h (struct tui_gen_win_info)
	(struct tui_data_window, struct tui_cmd_window) <refresh_window>:
	New method.