Standardize usage of virtual/override/final in sync/

sync/internal_api/js_mutation_event_observer.h

Index: sync/internal_api/js_mutation_event_observer.h
diff --git a/sync/internal_api/js_mutation_event_observer.h b/sync/internal_api/js_mutation_event_observer.h
index 5a007cbdc92dc1a77b56aa2fccb3c841bec85277..41bd9fab4f7fdc76b2983eeb279683209adda77c 100644
--- a/sync/internal_api/js_mutation_event_observer.h
+++ b/sync/internal_api/js_mutation_event_observer.h
@@ -34,7 +34,7 @@ class SYNC_EXPORT_PRIVATE JsMutationEventObserver
  public:
   JsMutationEventObserver();
 
-  virtual ~JsMutationEventObserver();
+  ~JsMutationEventObserver() override;
 
   base::WeakPtr<JsMutationEventObserver> AsWeakPtr();
 
@@ -43,14 +43,13 @@ class SYNC_EXPORT_PRIVATE JsMutationEventObserver
   void SetJsEventHandler(const WeakHandle<JsEventHandler>& event_handler);
 
   // SyncManager::ChangeObserver implementation.
-  virtual void OnChangesApplied(
-      ModelType model_type,
-      int64 write_transaction_id,
-      const ImmutableChangeRecordList& changes) override;
-  virtual void OnChangesComplete(ModelType model_type) override;
+  void OnChangesApplied(ModelType model_type,
+                        int64 write_transaction_id,
+                        const ImmutableChangeRecordList& changes) override;
+  void OnChangesComplete(ModelType model_type) override;
 
   // syncable::TransactionObserver implementation.
-  virtual void OnTransactionWrite(
+  void OnTransactionWrite(
       const syncable::ImmutableWriteTransactionInfo& write_transaction_info,
       ModelTypeSet models_with_changes) override;