[SyncFS] Use nullptr instead of NULL

chrome/browser/sync_file_system/file_change.cc

 // Copyright 2013 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 <sstream>
 
 #include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "chrome/browser/sync_file_system/file_change.h"
 
 namespace sync_file_system {
 
 FileChange::FileChange(
     ChangeType change,
     SyncFileType file_type)
     : change_(change),
       file_type_(file_type) {}
 
 std::string FileChange::DebugString() const {
-  const char* change_string = NULL;
+  const char* change_string = nullptr;
   switch (change()) {
     case FILE_CHANGE_ADD_OR_UPDATE:
       change_string = "ADD_OR_UPDATE";
       break;
     case FILE_CHANGE_DELETE:
       change_string = "DELETE";
       break;
   }
   const char* type_string = "UNKNOWN";
   switch (file_type()) {
@@ skipping 49 matching lines @@
 std::string FileChangeList::DebugString() const {
   std::ostringstream ss;
   ss << "{ ";
   for (size_t i = 0; i < list_.size(); ++i)
     ss << list_[i].DebugString() << ", ";
   ss << "}";
   return ss.str();
 }
 
 }  // namespace sync_file_system