Add scale support

tests/renderer-fps-test.c

@@ -109,6 +109,7 @@ int main(int argc, char **argv)
 	struct owb_config_header config = {
 		.magic = OWB_CONFIG_MAGIC, .version = OWB_PROTOCOL_VERSION,
 		.width = width, .height = height, .fps = requested_fps, .transparent = 1,
+		.zoom_percent = 100,
 		.hardware_acceleration = 1,
 		.url_length = sizeof(url) - 1, .css_length = (uint32_t)css_length,
 	};