NTP checks for guest sessions before updating the login bar.

chrome/browser/ui/webui/ntp/ntp_login_handler.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/webui/ntp/ntp_login_handler.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 155 matching lines @@
 
 void NTPLoginHandler::HandleShowAdvancedLoginUI(const base::ListValue* args) {
   Browser* browser =
       chrome::FindBrowserWithWebContents(web_ui()->GetWebContents());
   if (browser)
     chrome::ShowBrowserSignin(browser, signin_metrics::SOURCE_NTP_LINK);
 }
 
 void NTPLoginHandler::UpdateLogin() {
   Profile* profile = Profile::FromWebUI(web_ui());
+  if (profile->IsGuestSession())
+    return;
+
   std::string username =
       SigninManagerFactory::GetForProfile(profile)->GetAuthenticatedUsername();

[Dan Beam, 2015/03/18 17:08:09]

auto* factory = SigninManagerFactory::GetForProfile(profile);
if (!factory) {
  // Happens in guest mode.
  return;
}

[Mike Lerman, 2015/03/18 19:23:47]

Done.

 
   base::string16 header, sub_header;
   std::string icon_url;
   if (!username.empty()) {
     ProfileInfoCache& cache =
         g_browser_process->profile_manager()->GetProfileInfoCache();
     size_t profile_index = cache.GetIndexOfProfileWithPath(profile->GetPath());
     if (profile_index != std::string::npos) {
       // Only show the profile picture and full name for the single profile
       // case. In the multi-profile case the profile picture is visible in the
@@ skipping 65 matching lines @@
   values->SetString("login_status_message", message);
   values->SetString("login_status_url",
       hide_sync ? std::string() : chrome::kSyncLearnMoreURL);
   values->SetString("login_status_advanced",
       hide_sync ? base::string16() :
       l10n_util::GetStringUTF16(IDS_SYNC_PROMO_NTP_BUBBLE_ADVANCED));
   values->SetString("login_status_dismiss",
       hide_sync ? base::string16() :
       l10n_util::GetStringUTF16(IDS_SYNC_PROMO_NTP_BUBBLE_OK));
 }