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

chrome/browser/chromeos/printing/printer_pref_manager_factory.cc

 // Copyright 2016 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/chromeos/printing/printer_pref_manager_factory.h"
 
 #include "chrome/browser/profiles/profile.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 #include "content/public/browser/browser_context.h"
 
 namespace chromeos {
 
 namespace {
 
 base::LazyInstance<PrinterPrefManagerFactory> g_printer_pref_manager =
     LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 // static
 PrinterPrefManager* PrinterPrefManagerFactory::GetForBrowserContext(
     content::BrowserContext* context) {
+  DCHECK(!context->IsOffTheRecord());
   return static_cast<PrinterPrefManager*>(
       GetInstance()->GetServiceForBrowserContext(context, true));
 }
 
 // static
 PrinterPrefManagerFactory* PrinterPrefManagerFactory::GetInstance() {
   return g_printer_pref_manager.Pointer();
 }
 
 PrinterPrefManagerFactory::PrinterPrefManagerFactory()
     : BrowserContextKeyedServiceFactory(
           "PrinterPrefManager",
           BrowserContextDependencyManager::GetInstance()) {}
 
 PrinterPrefManagerFactory::~PrinterPrefManagerFactory() {}
 
 PrinterPrefManager* PrinterPrefManagerFactory::BuildServiceInstanceFor(
     content::BrowserContext* browser_context) const {
   Profile* profile = Profile::FromBrowserContext(browser_context);
   return new PrinterPrefManager(profile);
 }
 
 }  // namespace chromeos