Fixes the crash when the transient parent is NULL.

chrome/browser/ui/libgtk2ui/print_dialog_gtk2.cc

 // Copyright 2014 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 "chrome/browser/ui/libgtk2ui/print_dialog_gtk2.h"
 
 #include <gtk/gtkunixprint.h>
 
 #include <string>
 #include <vector>
@@ skipping 223 matching lines @@
 }
 
 void PrintDialogGtk2::ShowDialog(
     gfx::NativeView parent_view,
     bool has_selection,
     const PrintingContextLinux::PrintSettingsCallback& callback) {
   callback_ = callback;
 
   dialog_ = gtk_print_unix_dialog_new(NULL, NULL);
   libgtk2ui::SetGtkTransientForAura(dialog_, parent_view);
-  parent_view->AddObserver(this);
+  if (parent_view)
+    parent_view->AddObserver(this);
   g_signal_connect(dialog_, "delete-event",
                    G_CALLBACK(gtk_widget_hide_on_delete), NULL);
 
 
   // Set modal so user cannot focus the same tab and press print again.
   gtk_window_set_modal(GTK_WINDOW(dialog_), TRUE);
 
   // Since we only generate PDF, only show printers that support PDF.
   // TODO(thestig) Add more capabilities to support?
   GtkPrintCapabilities cap = static_cast<GtkPrintCapabilities>(
@@ skipping 186 matching lines @@
   context_->InitWithSettings(*settings);
 }
 
 void PrintDialogGtk2::OnWindowDestroying(aura::Window* window) {
   DCHECK_EQ(libgtk2ui::GetAuraTransientParent(dialog_), window);
 
   libgtk2ui::ClearAuraTransientParent(dialog_);
   window->RemoveObserver(this);
   Release();
 }