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

components/sync/model/fake_syncable_service.h

 // Copyright (c) 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.
 
 #ifndef COMPONENTS_SYNC_MODEL_FAKE_SYNCABLE_SERVICE_H_
 #define COMPONENTS_SYNC_MODEL_FAKE_SYNCABLE_SERVICE_H_
 
 #include <memory>
 
 #include "components/sync/model/syncable_service.h"
@@ skipping 10 matching lines @@
   ~FakeSyncableService() override;
 
   // Setters for SyncableService implementation results.
   void set_merge_data_and_start_syncing_error(const SyncError& error);
   void set_process_sync_changes_error(const SyncError& error);
 
   // Setter for AttachmentStore.
   void set_attachment_store(std::unique_ptr<AttachmentStore> attachment_store);
 
   // AttachmentService should be set when this syncable service is connected,
-  // just before MergeDataAndStartSyncing. NULL is returned by default.
+  // just before MergeDataAndStartSyncing. Null is returned by default.
   const AttachmentService* attachment_service() const;
 
   // Whether we're syncing or not. Set on a successful MergeDataAndStartSyncing,
   // unset on StopSyncing. False by default.
   bool syncing() const;
 
   // SyncableService implementation.
   SyncMergeResult MergeDataAndStartSyncing(
       ModelType type,
       const SyncDataList& initial_sync_data,
@@ skipping 13 matching lines @@
   SyncError process_sync_changes_error_;
   bool syncing_;
   ModelType type_;
   std::unique_ptr<AttachmentStore> attachment_store_;
   std::unique_ptr<AttachmentService> attachment_service_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_FAKE_SYNCABLE_SERVICE_H_