Standardize usage of virtual/override/final in chrome/browser/sync_file_system/

chrome/browser/sync_file_system/drive_backend/sync_task_manager.cc

Index: chrome/browser/sync_file_system/drive_backend/sync_task_manager.cc
diff --git a/chrome/browser/sync_file_system/drive_backend/sync_task_manager.cc b/chrome/browser/sync_file_system/drive_backend/sync_task_manager.cc
index f51f36d678b6defb6e5b8b4f84a361ec9f50435e..d6ecbae566798c7639729b29cb39acfbae907ac4 100644
--- a/chrome/browser/sync_file_system/drive_backend/sync_task_manager.cc
+++ b/chrome/browser/sync_file_system/drive_backend/sync_task_manager.cc
@@ -22,9 +22,9 @@ namespace {
 class SyncTaskAdapter : public ExclusiveTask {
  public:
   explicit SyncTaskAdapter(const SyncTaskManager::Task& task) : task_(task) {}
-  virtual ~SyncTaskAdapter() {}
+  ~SyncTaskAdapter() override {}
 
-  virtual void RunExclusive(const SyncStatusCallback& callback) override {
+  void RunExclusive(const SyncStatusCallback& callback) override {
     task_.Run(callback);
   }