Use override & final instead of just using virtual.

This is safer than using virtual and this lead to a minor
bug fixes.

Change-Id: Id69cb1cc569bf6bf245f22f029c7871b6c712568

internal/ceres/compressed_row_sparse_matrix_test.cc

@@ -71,7 +71,7 @@ static void CompareMatrices(const SparseMatrix* a, const SparseMatrix* b) {
 
 class CompressedRowSparseMatrixTest : public ::testing::Test {
  protected:
-  virtual void SetUp() {
+  void SetUp() final {
     std::unique_ptr<LinearLeastSquaresProblem> problem(
         CreateLinearLeastSquaresProblemFromId(1));