Force guest profiles to return default startup prefs.

chrome/browser/prefs/session_startup_pref.cc

Index: chrome/browser/prefs/session_startup_pref.cc
diff --git a/chrome/browser/prefs/session_startup_pref.cc b/chrome/browser/prefs/session_startup_pref.cc
index 9126203deeba9a3b95501a654cc9d16baccc036e..1b569b08b765c9629e086e124c4b9281a83634a5 100644
--- a/chrome/browser/prefs/session_startup_pref.cc
+++ b/chrome/browser/prefs/session_startup_pref.cc
@@ -99,7 +99,12 @@ void SessionStartupPref::SetStartupPref(PrefService* prefs,
 // static
 SessionStartupPref SessionStartupPref::GetStartupPref(Profile* profile) {
   DCHECK(profile);
-  return GetStartupPref(profile->GetPrefs());
+
+  // Guest sessions should not store any state, therefore they should never
+  // trigger a restore during startup.
+  return profile->IsGuestSession()
+             ? SessionStartupPref(SessionStartupPref::DEFAULT)
+             : GetStartupPref(profile->GetPrefs());
 }
 
 // static