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

components/sync/model/syncable_service.h

 // 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.
 
 #ifndef COMPONENTS_SYNC_MODEL_SYNCABLE_SERVICE_H_
 #define COMPONENTS_SYNC_MODEL_SYNCABLE_SERVICE_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 49 matching lines @@
   // Process a list of new SyncChanges and update the local data as necessary.
   // Returns: A default SyncError (IsSet() == false) if no errors were
   //          encountered, and a filled SyncError (IsSet() == true)
   //          otherwise.
   SyncError ProcessSyncChanges(const tracked_objects::Location& from_here,
                                const SyncChangeList& change_list) override = 0;
 
   // Returns AttachmentStore for use by sync when uploading or downloading
   // attachments.
   // GetAttachmentStoreForSync is called right before MergeDataAndStartSyncing.
-  // If at that time GetAttachmentStoreForSync returns NULL then datatype is
+  // If at that time GetAttachmentStoreForSync returns null then datatype is
   // considered not using attachments and all attempts to upload/download
-  // attachments will fail. Default implementation returns NULL. Datatype that
+  // attachments will fail. Default implementation returns null. Datatype that
   // uses sync attachments should create attachment store, implement
   // GetAttachmentStoreForSync to return result of
   // AttachmentStore::CreateAttachmentStoreForSync() from attachment store
   // object.
   virtual std::unique_ptr<AttachmentStoreForSync> GetAttachmentStoreForSync();
 
   // Called by sync to provide AttachmentService to be used to download
   // attachments.
   // SetAttachmentService is called after GetAttachmentStore and right before
   // MergeDataAndStartSyncing and only if GetAttachmentStore has returned a
-  // non-NULL store instance. Default implementation does nothing.
+  // non-null store instance. Default implementation does nothing.
   // Datatype that uses attachments must take ownerhip of the provided
   // AttachmentService instance.
   virtual void SetAttachmentService(
       std::unique_ptr<AttachmentService> attachment_service);
 
  protected:
   ~SyncableService() override;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_SYNCABLE_SERVICE_H_