Standardize usage of virtual/override/final in sync/

sync/internal_api/public/attachments/on_disk_attachment_store.h

Index: sync/internal_api/public/attachments/on_disk_attachment_store.h
diff --git a/sync/internal_api/public/attachments/on_disk_attachment_store.h b/sync/internal_api/public/attachments/on_disk_attachment_store.h
index d74b60bf60895fe66b56a1d1df9052fc83c685db..fad362f8ca17d1215c7386096bdda89e89bb98c4 100644
--- a/sync/internal_api/public/attachments/on_disk_attachment_store.h
+++ b/sync/internal_api/public/attachments/on_disk_attachment_store.h
@@ -31,18 +31,16 @@ class SYNC_EXPORT OnDiskAttachmentStore : public AttachmentStoreBase,
   // Constructs attachment store.
   OnDiskAttachmentStore(
       const scoped_refptr<base::SequencedTaskRunner>& callback_task_runner);
-  virtual ~OnDiskAttachmentStore();
+  ~OnDiskAttachmentStore() override;
 
   // AttachmentStoreBase implementation.
   // Load opens database, creating it if needed. In the future upgrade code will
   // be invoked from Load as well. If loading fails it posts |callback| with
   // UNSPECIFIED_ERROR.
-  virtual void Read(const AttachmentIdList& ids,
-                    const ReadCallback& callback) override;
-  virtual void Write(const AttachmentList& attachments,
-                     const WriteCallback& callback) override;
-  virtual void Drop(const AttachmentIdList& ids,
-                    const DropCallback& callback) override;
+  void Read(const AttachmentIdList& ids, const ReadCallback& callback) override;
+  void Write(const AttachmentList& attachments,
+             const WriteCallback& callback) override;
+  void Drop(const AttachmentIdList& ids, const DropCallback& callback) override;
 
   // Opens leveldb database at |path|. It will create directory and database if
   // it doesn't exist.