Change tui_update_source_window_as_is to be a method

Change tui_update_source_window_as_is to be a method

This changes tui_update_source_window_as_is to be a method on
tui_source_window_base.

gdb/ChangeLog
2019-08-16  Tom Tromey  <tom@tromey.com>

	* tui/tui-winsource.h (struct tui_source_window_base)
	<update_source_window_as_is>: Declare.
	(tui_update_source_window_as_is): Don't declare.
	* tui/tui-winsource.c (tui_update_source_window): Update
	(tui_source_window_base::update_source_window_as_is): Rename from
	tui_update_source_window_as_is.
	(tui_source_window_base::refill): Update.
	* tui/tui-source.c (tui_show_symtab_source): Update.
	* tui/tui-disasm.c (tui_disasm_window::do_scroll_vertical):
	Update.