patch 8.1.1525: cannot move a popup window with the mouse
Problem: Cannot move a popup window with the mouse.
Solution: Add the "drag" property and make it possible to drag a popup
window by its border.
diff --git a/src/proto/window.pro b/src/proto/window.pro
index 1424c3d..94b9f08 100644
--- a/src/proto/window.pro
+++ b/src/proto/window.pro
@@ -3,6 +3,7 @@
void get_wincmd_addr_type(char_u *arg, exarg_T *eap);
int win_split(int size, int flags);
int win_split_ins(int size, int flags, win_T *new_wp, int dir);
+int win_valid_popup(win_T *win);
int win_valid(win_T *win);
int win_valid_any_tab(win_T *win);
int win_count(void);