Standardize usage of virtual/override/final specifiers in sync/.

sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc

Index: sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc
diff --git a/sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc b/sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc
index b58ccb7624bd2c8cc8e198a1bc91257c33af408b..fbba75e537ce0700a8f3984aa862f57bb2a3e0f9 100644
--- a/sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc
+++ b/sync/syncable/deferred_on_disk_directory_backing_store_unittest.cc
@@ -20,14 +20,12 @@ static const base::FilePath::CharType kSyncDataFolderName[] =
 
 class DeferredOnDiskDirectoryBackingStoreTest : public testing::Test {
  protected:
-  virtual void SetUp() override {
+  void SetUp() override {
     CHECK(temp_dir_.CreateUniqueTempDir());
     db_path_ = temp_dir_.path().Append(kSyncDataFolderName);
   }
 
-  virtual void TearDown() override {
-    STLDeleteValues(&handles_map_);
-  }
+  void TearDown() override { STLDeleteValues(&handles_map_); }
 
   base::ScopedTempDir temp_dir_;
   base::FilePath db_path_;