clients: Maximize window when double click on title bar

Signed-off-by: Xiong Zhang <panda0626@gmail.com>
Tested-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/shared/cairo-util.h b/shared/cairo-util.h
index fb25c34..99c7736 100644
--- a/shared/cairo-util.h
+++ b/shared/cairo-util.h
@@ -213,6 +213,10 @@
 void
 frame_touch_up(struct frame *frame, void *data, int32_t id);
 
+enum theme_location
+frame_double_click(struct frame *frame, void *pointer,
+		   uint32_t button, enum frame_button_state state);
+
 void
 frame_repaint(struct frame *frame, cairo_t *cr);