Defer window destruction until GPU finished drawing.

gfx/gtk_preserve_window.cc

Index: gfx/gtk_preserve_window.cc
diff --git a/gfx/gtk_preserve_window.cc b/gfx/gtk_preserve_window.cc
index c49bd31531880e1f1e13a1309701bb32c182c442..0e2b9db87fdded0ca02ff4b3969bc1daf12bb7bc 100644
--- a/gfx/gtk_preserve_window.cc
+++ b/gfx/gtk_preserve_window.cc
@@ -61,10 +61,13 @@ GtkWidget* gtk_preserve_window_new() {
 
 static void gtk_preserve_window_destroy(GtkObject* object) {
   GtkWidget* widget = reinterpret_cast<GtkWidget*>(object);
+  GtkPreserveWindowPrivate* priv = GTK_PRESERVE_WINDOW_GET_PRIVATE(widget);
 
   if (widget->window) {
     gdk_window_set_user_data(widget->window, NULL);
-    gdk_window_destroy(widget->window);
+    // If the window is preserved, someone else must destroy it.
+    if (!priv->preserve_window)
+      gdk_window_destroy(widget->window);
     widget->window = NULL;
   }