[mutter/gnome-3-36] x11: Only send SelectionNotify on first INCR chunk

[Robert Mader <rmader src gnome org>]

commit 622e8c348f019527034599a2fa3c7ed8f0be3971
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Apr 11 17:05:24 2020 +0200

    x11: Only send SelectionNotify on first INCR chunk
    
    This should only be sent if the selection can be sent at once, or
    if we are right about to notify on the first chunk of an INCR
    transfer.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1198
    
    (cherry picked from commit 7c939d78c2b20989412a710665cbbea6b12ff8dd)

 src/x11/meta-x11-selection-output-stream.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/src/x11/meta-x11-selection-output-stream.c b/src/x11/meta-x11-selection-output-stream.c
index 7ae1e1acc..f7c27cc09 100644
--- a/src/x11/meta-x11-selection-output-stream.c
+++ b/src/x11/meta-x11-selection-output-stream.c
@@ -199,6 +199,7 @@ meta_x11_selection_output_stream_perform_flush (MetaX11SelectionOutputStream *st
     meta_x11_selection_output_stream_get_instance_private (stream);
   Display *xdisplay;
   size_t element_size, n_elements;
+  gboolean first_chunk = FALSE;
   int error_code;
 
   g_assert (!priv->delete_pending);
@@ -213,6 +214,9 @@ meta_x11_selection_output_stream_perform_flush (MetaX11SelectionOutputStream *st
   element_size = get_element_size (priv->format);
   n_elements = priv->data->len / element_size;
 
+  if (!priv->incr)
+    first_chunk = TRUE;
+
   if (!g_output_stream_is_closing (G_OUTPUT_STREAM (stream)))
     {
       XWindowAttributes attrs;
@@ -248,7 +252,8 @@ meta_x11_selection_output_stream_perform_flush (MetaX11SelectionOutputStream *st
       g_byte_array_remove_range (priv->data, 0, n_elements * element_size);
     }
 
-  meta_x11_selection_output_stream_notify_selection (stream);
+  if (first_chunk)
+    meta_x11_selection_output_stream_notify_selection (stream);
 
   priv->delete_pending = TRUE;
   g_cond_broadcast (&priv->cond);