Standardize usage of virtual/override/final in sync/

sync/syncable/directory_backing_store_unittest.cc

Index: sync/syncable/directory_backing_store_unittest.cc
diff --git a/sync/syncable/directory_backing_store_unittest.cc b/sync/syncable/directory_backing_store_unittest.cc
index 804fa98ad3488f01ae018e9144f234c07065997f..9b92e56719404e01a04ac390de741b589c88cbe9 100644
--- a/sync/syncable/directory_backing_store_unittest.cc
+++ b/sync/syncable/directory_backing_store_unittest.cc
@@ -3836,11 +3836,11 @@ class OnDiskDirectoryBackingStoreForTest : public OnDiskDirectoryBackingStore {
  public:
   OnDiskDirectoryBackingStoreForTest(const std::string& dir_name,
                                      const base::FilePath& backing_filepath);
-  virtual ~OnDiskDirectoryBackingStoreForTest();
+  ~OnDiskDirectoryBackingStoreForTest() override;
   bool DidFailFirstOpenAttempt();
 
  protected:
-  virtual void ReportFirstTryOpenFailure() override;
+  void ReportFirstTryOpenFailure() override;
 
  private:
   bool first_open_failed_;