[CUPS] Fix the browser crash in CUPS settings UI in guest mode.

chrome/browser/chromeos/printing/printer_pref_manager_factory.cc

Index: chrome/browser/chromeos/printing/printer_pref_manager_factory.cc
diff --git a/chrome/browser/chromeos/printing/printer_pref_manager_factory.cc b/chrome/browser/chromeos/printing/printer_pref_manager_factory.cc
index 43c1bec267c8d8714fa8abae20c6ffd799e2b803..e70ef4f4eb0a206ad1ba030af74b5259d689aa86 100644
--- a/chrome/browser/chromeos/printing/printer_pref_manager_factory.cc
+++ b/chrome/browser/chromeos/printing/printer_pref_manager_factory.cc
@@ -20,6 +20,7 @@ base::LazyInstance<PrinterPrefManagerFactory> g_printer_pref_manager =
 // static
 PrinterPrefManager* PrinterPrefManagerFactory::GetForBrowserContext(
     content::BrowserContext* context) {
+  DCHECK(!context->IsOffTheRecord());
   return static_cast<PrinterPrefManager*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }