Standardize usage of virtual/override/final in sync/

sync/syncable/invalid_directory_backing_store.h

Index: sync/syncable/invalid_directory_backing_store.h
diff --git a/sync/syncable/invalid_directory_backing_store.h b/sync/syncable/invalid_directory_backing_store.h
index dbd6500d5a8db28f9479a05ddc1ee4a871384390..fd99653a3f77d641a22fcd80dea8f939f16d5a32 100644
--- a/sync/syncable/invalid_directory_backing_store.h
+++ b/sync/syncable/invalid_directory_backing_store.h
@@ -16,11 +16,11 @@ class SYNC_EXPORT_PRIVATE InvalidDirectoryBackingStore
     : public DirectoryBackingStore {
  public:
   InvalidDirectoryBackingStore();
-  virtual ~InvalidDirectoryBackingStore();
-  virtual DirOpenResult Load(
-      Directory::MetahandlesMap* handles_map,
-      JournalIndex* delete_journals,
-      Directory::KernelLoadInfo* kernel_load_info) override;
+  ~InvalidDirectoryBackingStore() override;
+  DirOpenResult Load(Directory::MetahandlesMap* handles_map,
+                     JournalIndex* delete_journals,
+                     Directory::KernelLoadInfo* kernel_load_info) override;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(InvalidDirectoryBackingStore);
 };