[SyncFS] Use nullptr instead of NULL

chrome/browser/sync_file_system/drive_backend/leveldb_wrapper_unittest.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/sync_file_system/drive_backend/leveldb_wrapper.h"
 
 #include <string>
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
@@ skipping 52 matching lines @@
       ASSERT_TRUE(itr->Valid());
       EXPECT_EQ(expects[i].key, itr->key().ToString());
       EXPECT_EQ(expects[i].value, itr->value().ToString());
       itr->Next();
     }
     EXPECT_FALSE(itr->Valid());
   }
 
  private:
   void InitializeLevelDB() {
-    leveldb::DB* db = NULL;
+    leveldb::DB* db = nullptr;
     leveldb::Options options;
     options.create_if_missing = true;
     options.max_open_files = 0;  // Use minimum.
     options.env = in_memory_env_.get();
     leveldb::Status status =
         leveldb::DB::Open(options, database_dir_.path().AsUTF8Unsafe(), &db);
     ASSERT_TRUE(status.ok());
 
     db_.reset(new LevelDBWrapper(make_scoped_ptr(db)));
   }
@@ skipping 148 matching lines @@
 
   EXPECT_EQ(0, GetDB()->num_puts());
   EXPECT_EQ(0, GetDB()->num_deletes());
 
   SCOPED_TRACE("DeleteTest_Commit");
   CheckDBContents(merged_data, arraysize(merged_data));
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system