[Password Manager Cleanup] Replaces NULL -> nullptr.

chrome/browser/password_manager/mock_password_store_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 "chrome/browser/password_manager/mock_password_store_service.h"
 
 #include "components/password_manager/core/browser/mock_password_store.h"
 
 // static
 KeyedService* MockPasswordStoreService::Build(
     content::BrowserContext* /*profile*/) {
   scoped_refptr<password_manager::PasswordStore> store(
       new password_manager::MockPasswordStore);
   if (!store.get() || !store->Init(syncer::SyncableService::StartSyncFlare()))
-    return NULL;
+    return nullptr;
   return new MockPasswordStoreService(store);
 }
 
 MockPasswordStoreService::MockPasswordStoreService(
     scoped_refptr<password_manager::PasswordStore> password_store)
     : PasswordStoreService(password_store) {}
 
 MockPasswordStoreService::~MockPasswordStoreService() {}