Fix crash in aura::Window::GetHost

chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc

Index: chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc
diff --git a/chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc b/chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc
index d37f9be03c1e32e364f41512be8e72cbd2f3e610..5ccff627f91b2272c323b613989a4caa8160a828 100644
--- a/chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc
+++ b/chrome/browser/ui/libgtk2ui/select_file_dialog_impl_gtk2.cc
@@ -170,16 +170,18 @@ void SelectFileDialogImplGTK::SelectFileImpl(
   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);