compositor: add scale cmdline option for headless

The test suite wants to start using different output scales, and this is the
easiest API to configure it.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

compositor/main.c

@@ -687,6 +687,7 @@ usage(int error_code)
 		"Options for headless-backend.so:\n\n"
 		"  --width=WIDTH\t\tWidth of memory surface\n"
 		"  --height=HEIGHT\tHeight of memory surface\n"
+		"  --scale=SCALE\t\tScale factor of output\n"
 		"  --transform=TR\tThe output transformation, TR is one of:\n"
 		"\tnormal 90 180 270 flipped flipped-90 flipped-180 flipped-270\n"
 		"  --use-pixman\t\tUse the pixman (CPU) renderer (default: no rendering)\n"
@@ -2567,6 +2568,7 @@ load_headless_backend(struct weston_compositor *c,
 	const struct weston_option options[] = {
 		{ WESTON_OPTION_INTEGER, "width", 0, &parsed_options->width },
 		{ WESTON_OPTION_INTEGER, "height", 0, &parsed_options->height },
+		{ WESTON_OPTION_INTEGER, "scale", 0, &parsed_options->scale },
 		{ WESTON_OPTION_BOOLEAN, "use-pixman", 0, &config.use_pixman },
 		{ WESTON_OPTION_BOOLEAN, "use-gl", 0, &config.use_gl },
 		{ WESTON_OPTION_STRING, "transform", 0, &transform },