Fix crash/leak issue in native_view_host_gtk.cc.

views/controls/native_control_gtk.cc

Index: views/controls/native_control_gtk.cc
diff --git a/views/controls/native_control_gtk.cc b/views/controls/native_control_gtk.cc
index 49453efe71380f7bf0ce9f20732a05462682e50f..66e6994358b806e7c6561e4194f32fa58ef32d2a 100644
--- a/views/controls/native_control_gtk.cc
+++ b/views/controls/native_control_gtk.cc
@@ -49,9 +49,9 @@ void NativeControlGtk::VisibilityChanged(View* starting_from, bool is_visible) {
     if (native_view()) {
       // We destroy the child widget when we become invisible because of the
       // performance cost of maintaining widgets that aren't currently needed.
-      GtkWidget* widget = native_view();
       Detach();
-      gtk_widget_destroy(widget);
+      // Make sure that Detach destroyed the widget.
+      DCHECK(!native_view());
     }
   } else if (!native_view()) {
     if (GetWidget())