Fix crash in aura::Window::GetHost

chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc

 // Copyright (c) 2012 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/select_file_dialog_impl_gtk2.h"
 
 #include <gdk/gdkx.h>
 #include <gtk/gtk.h>
 #include <stddef.h>
 #include <sys/stat.h>
@@ skipping 152 matching lines @@
   preview_ = gtk_image_new();
   g_signal_connect(dialog, "destroy",
                    G_CALLBACK(OnFileChooserDestroyThunk), this);
   g_signal_connect(dialog, "update-preview",
                    G_CALLBACK(OnUpdatePreviewThunk), this);
   gtk_file_chooser_set_preview_widget(GTK_FILE_CHOOSER(dialog), preview_);
 
   params_map_[dialog] = params;
 
   // Disable input events handling in the host window to make this dialog modal.
-  views::DesktopWindowTreeHostX11* host =
-      views::DesktopWindowTreeHostX11::GetHostForXID(
-      owning_window->GetHost()->GetAcceleratedWidget());
-  std::unique_ptr<base::Closure> callback = host->DisableEventListening(
-      GDK_WINDOW_XID(gtk_widget_get_window(dialog)));
-  // OnFilePickerDestroy() is called when |dialog| destroyed, which allows to
-  // invoke the callback function to re-enable events on the owning window.
-  g_object_set_data_full(G_OBJECT(dialog), "callback", callback.release(),
-      reinterpret_cast<GDestroyNotify>(OnFilePickerDestroy));
-  gtk_window_set_modal(GTK_WINDOW(dialog), TRUE);
+  aura::WindowTreeHost* host = owning_window->GetHost();
+  if (host) {
+    std::unique_ptr<base::Closure> callback =
+        views::DesktopWindowTreeHostX11::GetHostForXID(
+        host->GetAcceleratedWidget())->DisableEventListening(
+        GDK_WINDOW_XID(gtk_widget_get_window(dialog)));
+    // OnFilePickerDestroy() is called when |dialog| destroyed, which allows to
+    // invoke the callback function to re-enable events on the owning window.
+    g_object_set_data_full(G_OBJECT(dialog), "callback", callback.release(),
+        reinterpret_cast<GDestroyNotify>(OnFilePickerDestroy));
+    gtk_window_set_modal(GTK_WINDOW(dialog), TRUE);
+  }
 
   gtk_widget_show_all(dialog);
 
   // We need to call gtk_window_present after making the widgets visible to make
   // sure window gets correctly raised and gets focus.
   gtk_window_present_with_time(
       GTK_WINDOW(dialog), ui::X11EventSource::GetInstance()->GetTimestamp());
 }
 
 void SelectFileDialogImplGTK::AddFilters(GtkFileChooser* chooser) {
@@ skipping 354 matching lines @@
   g_free(filename);
   if (pixbuf) {
     gtk_image_set_from_pixbuf(GTK_IMAGE(preview_), pixbuf);
     g_object_unref(pixbuf);
   }
   gtk_file_chooser_set_preview_widget_active(GTK_FILE_CHOOSER(chooser),
                                              pixbuf ? TRUE : FALSE);
 }
 
 }  // namespace libgtk2ui