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

base/metrics/sparse_histogram_unittest.cc

Index: base/metrics/sparse_histogram_unittest.cc
diff --git a/base/metrics/sparse_histogram_unittest.cc b/base/metrics/sparse_histogram_unittest.cc
index 6a0efa4e12b616cc28229076edc5011b4662c75d..c29dd5e22549dccf5143e606d7e650d61668184d 100644
--- a/base/metrics/sparse_histogram_unittest.cc
+++ b/base/metrics/sparse_histogram_unittest.cc
@@ -18,15 +18,13 @@ namespace base {
 
 class SparseHistogramTest : public testing::Test {
  protected:
-  virtual void SetUp() {
+  void SetUp() override {
     // Each test will have a clean state (no Histogram / BucketRanges
     // registered).
     InitializeStatisticsRecorder();
   }
 
-  virtual void TearDown() {
-    UninitializeStatisticsRecorder();
-  }
+  void TearDown() override { UninitializeStatisticsRecorder(); }
 
   void InitializeStatisticsRecorder() {
     statistics_recorder_ = new StatisticsRecorder();