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

base/metrics/histogram_base_unittest.cc

Index: base/metrics/histogram_base_unittest.cc
diff --git a/base/metrics/histogram_base_unittest.cc b/base/metrics/histogram_base_unittest.cc
index 4a2963aa6c4034ce5adec6cfbf2f2e19883aee23..2d6b6df0288850cab31362762957070201ca72e3 100644
--- a/base/metrics/histogram_base_unittest.cc
+++ b/base/metrics/histogram_base_unittest.cc
@@ -22,9 +22,7 @@ class HistogramBaseTest : public testing::Test {
     ResetStatisticsRecorder();
   }
 
-  virtual ~HistogramBaseTest() {
-    delete statistics_recorder_;
-  }
+  ~HistogramBaseTest() override { delete statistics_recorder_; }
 
   void ResetStatisticsRecorder() {
     delete statistics_recorder_;