Do not crash if no Account Info Preferences exist

components/signin/core/browser/account_tracker_service.cc

 // Copyright 2014 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 "components/signin/core/browser/account_tracker_service.h"
 
 #include <stddef.h>
 
 #include "base/callback.h"
 #include "base/command_line.h"
@@ skipping 290 matching lines @@
   for (std::map<std::string, AccountState>::const_iterator it =
            migrated_accounts.begin();
        it != migrated_accounts.end(); ++it) {
     accounts_.insert(*it);
   }
 }
 
 void AccountTrackerService::LoadFromPrefs() {
   const base::ListValue* list =
       signin_client_->GetPrefs()->GetList(kAccountInfoPref);
+  if (list == nullptr)
+    return;
   std::set<std::string> to_remove;
   bool contains_deprecated_service_flags = false;
   for (size_t i = 0; i < list->GetSize(); ++i) {
     const base::DictionaryValue* dict;
     if (list->GetDictionary(i, &dict)) {
       base::string16 value;
       if (dict->GetString(kAccountKeyPath, &value)) {
         std::string account_id = base::UTF16ToUTF8(value);
 
         // Ignore incorrectly persisted non-canonical account ids.
@@ skipping 180 matching lines @@
       NotifyAccountUpdated(state);
     }
     SaveToPrefs(state);
   }
   return info.account_id;
 }
 
 void AccountTrackerService::RemoveAccount(const std::string& account_id) {
   StopTrackingAccount(account_id);
 }