user32/msgbox: Implement MB_TOPMOST.

dlls/user32/msgbox.c

@@ -110,10 +110,12 @@ static void MSGBOX_OnInit(HWND hwnd, LPMSGBOXPARAMSW lpmb)
     }
 
     /* handle modal message boxes */
-    if (((lpmb->dwStyle & MB_TASKMODAL) && (lpmb->hwndOwner==NULL)))
-        NtUserSetWindowPos( hwnd, HWND_TOP, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE );
+    if (lpmb->dwStyle & MB_TASKMODAL && lpmb->hwndOwner == NULL)
+        NtUserSetWindowPos( hwnd, lpmb->dwStyle & MB_TOPMOST ? HWND_TOPMOST : HWND_TOP, 0, 0, 0, 0, SWP_NOSIZE | SWP_NOMOVE );
     else if (lpmb->dwStyle & MB_SYSTEMMODAL)
         NtUserSetWindowPos( hwnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_FRAMECHANGED );
+    else if (lpmb->dwStyle & MB_TOPMOST)
+        NtUserSetWindowPos( hwnd, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE );
 
     TRACE_(msgbox)("%s\n", debugstr_w(lpszText));
     SetWindowTextW(GetDlgItem(hwnd, MSGBOX_IDTEXT), lpszText);

dlls/user32/tests/dialog.c

@@ -2149,8 +2149,7 @@ static LRESULT CALLBACK msgbox_hook_proc(INT code, WPARAM wParam, LPARAM lParam)
             if (!system_modal)
                 expected_exstyles |= WS_EX_DLGMODALFRAME;
 
-            todo_wine_if((system_modal && exstyles == (expected_exstyles | WS_EX_DLGMODALFRAME))
-                    || (!system_modal && msgbox_type & MB_TOPMOST))
+            todo_wine_if(system_modal && exstyles == (expected_exstyles | WS_EX_DLGMODALFRAME))
             ok(exstyles == expected_exstyles, "got %#lx, expected %#lx\n", exstyles, expected_exstyles);
 
             text[0] = 0;