GTK: Adds #error statements to GTK code to root out unknown bots.

ui/base/gtk/owned_widget_gtk.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/base/gtk/owned_widget_gtk.h"
 
 #include <gtk/gtk.h>
 
 #include "base/logging.h"
 
+#error "The GTK+ port will be deleted later this week. If you are seeing this, you are trying to compile it. Please check your gyp flags for 'use_aura=0' and remove them."
+
 namespace ui {
 
 OwnedWidgetGtk::~OwnedWidgetGtk() {
   Destroy();
 }
 
 void OwnedWidgetGtk::Own(GtkWidget* widget) {
   if (!widget)
     return;
 
@@ skipping 15 matching lines @@
   widget_ = NULL;
   gtk_widget_destroy(widget);
 
   DCHECK(!g_object_is_floating(widget));
   // NOTE: Assumes some implementation details about glib internals.
   DCHECK_EQ(G_OBJECT(widget)->ref_count, 1U);
   g_object_unref(widget);
 }
 
 }  // namespace ui