entry: Allow entry to decide to not record undo actions

This is useful when recording would be nested (should not be happening
now, but might hppen once we add more API).

And more importantly, we don't want to allow undo for password entries.

gtk/gtkentry.c

@@ -5815,6 +5815,26 @@ struct _GtkEntryRecording {
   GtkEntrySnapshot snapshot;
 };
 
+static gboolean
+gtk_entry_should_record (GtkEntry *entry)
+{
+  GtkEntryPrivate *priv = entry->priv;
+
+  /* Password entries should not allow undo because
+   * the undo stack might otherwise contain sensitive
+   * information about passwords.
+   */
+  if (!priv->visible)
+    return FALSE;
+
+  /* Somebody is already recording and recording the same
+   * thing twice makes no sense. */
+  if (priv->undo_mode == GTK_ENTRY_UNDO_RECORD)
+    return FALSE;
+
+  return TRUE;
+}
+
 static GtkEntryRecording *
 gtk_entry_start_recording (GtkEntry *entry)
 {
@@ -5822,6 +5842,9 @@ gtk_entry_start_recording (GtkEntry *entry)
 
   g_return_val_if_fail (GTK_IS_ENTRY (entry), NULL);
 
+  if (!gtk_entry_should_record (entry))
+    return NULL;
+
   recording = g_slice_new0 (GtkEntryRecording);
   recording->old_mode = gtk_entry_set_undo_mode (entry, GTK_ENTRY_UNDO_RECORD);
   gtk_entry_snapshot_init_from_entry (&recording->snapshot, entry);
@@ -5835,7 +5858,9 @@ gtk_entry_end_recording (GtkEntry          *entry,
                          gboolean           commit)
 {
   g_return_if_fail (GTK_IS_ENTRY (entry));
-  g_return_if_fail (recording != NULL);
+
+  if (recording == NULL)
+    return;
 
   if (commit)
     {