[Sync] Replacing NULL with nullptr in code and null in comments for components/sync/

components/sync/syncable/write_transaction.cc

 // Copyright 2012 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/sync/syncable/write_transaction.h"
 
 #include "components/sync/syncable/directory.h"
 #include "components/sync/syncable/mutable_entry.h"
 #include "components/sync/syncable/syncable_write_transaction.h"
 
 namespace syncer {
 
 //////////////////////////////////////////////////////////////////////////
 // WriteTransaction member definitions
 WriteTransaction::WriteTransaction(const tracked_objects::Location& from_here,
                                    UserShare* share)
-    : BaseTransaction(share), transaction_(NULL) {
+    : BaseTransaction(share), transaction_(nullptr) {
   transaction_ = new syncable::WriteTransaction(from_here, syncable::SYNCAPI,
                                                 share->directory.get());
 }
 
 WriteTransaction::WriteTransaction(const tracked_objects::Location& from_here,
                                    UserShare* share,
                                    int64_t* new_model_version)
-    : BaseTransaction(share), transaction_(NULL) {
+    : BaseTransaction(share), transaction_(nullptr) {
   transaction_ = new syncable::WriteTransaction(
       from_here, share->directory.get(), new_model_version);
 }
 
 WriteTransaction::~WriteTransaction() {
   delete transaction_;
 }
 
 syncable::BaseTransaction* WriteTransaction::GetWrappedTrans() const {
   return transaction_;
@@ skipping 44 matching lines @@
   GetDirectory()->GetMetahandlesByAttachmentId(
       transaction_, attachment_id.GetProto(), &handles);
   for (syncable::Directory::Metahandles::iterator iter = handles.begin();
        iter != handles.end(); ++iter) {
     syncable::MutableEntry entry(transaction_, syncable::GET_BY_HANDLE, *iter);
     entry.MarkAttachmentAsOnServer(attachment_id.GetProto());
   }
 }
 
 }  // namespace syncer