Linux Printing: Add a CHECK to help track down a crash.

chrome/browser/printing/print_dialog_gtk.cc

 // Copyright (c) 2009 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/printing/print_dialog_gtk.h"
 
 #include <gtk/gtkprintjob.h>
 #include <gtk/gtkprintunixdialog.h>
 #include <gtk/gtkpagesetupunixdialog.h>
 
@@ skipping 107 matching lines @@
 }
 
 void PrintDialogGtk::OnResponse(GtkWidget* dialog, gint response_id) {
   gtk_widget_hide(dialog_);
 
   switch (response_id) {
     case GTK_RESPONSE_OK: {
       GtkPrinter* printer =
           gtk_print_unix_dialog_get_selected_printer(
               GTK_PRINT_UNIX_DIALOG(dialog_));
+      // Attempt to track down bug 70166.
+      CHECK(printer != NULL);
       if (!gtk_printer_accepts_pdf(printer)) {
         browser_->GetSelectedTabContents()->AddInfoBar(
             new PdfUnsupportedInfoBarDelegate(browser_));
         break;
       }
 
       GtkPrintSettings* settings =
           gtk_print_unix_dialog_get_settings(
               GTK_PRINT_UNIX_DIALOG(dialog_));
       GtkPageSetup* setup = gtk_print_unix_dialog_get_page_setup(
@@ skipping 39 matching lines @@
     g_object_unref(job);
 
   base::FileUtilProxy::Delete(
       BrowserThread::GetMessageLoopProxyForThread(BrowserThread::FILE),
       path_to_pdf_,
       false,
       NULL);
 
   delete this;
 }