Update {virtual,override} to follow C++11 style in sync.

sync/internal_api/sync_rollback_manager_unittest.cc

Index: sync/internal_api/sync_rollback_manager_unittest.cc
diff --git a/sync/internal_api/sync_rollback_manager_unittest.cc b/sync/internal_api/sync_rollback_manager_unittest.cc
index c03343df916be9c1d93070ef790b99ee4ca9cba8..31ffd14a21d82225b182481683d1c87e7f3cd54d 100644
--- a/sync/internal_api/sync_rollback_manager_unittest.cc
+++ b/sync/internal_api/sync_rollback_manager_unittest.cc
@@ -68,7 +68,7 @@ class TestChangeDelegate : public SyncManager::ChangeDelegate {
 class SyncRollbackManagerTest : public testing::Test,
                                 public SyncManager::Observer {
  protected:
-  virtual void SetUp() override {
+  void SetUp() override {
     CHECK(temp_dir_.CreateUniqueTempDir());
 
     worker_ = new FakeModelWorker(GROUP_UI);