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

base/metrics/histogram_unittest.cc

Index: base/metrics/histogram_unittest.cc
diff --git a/base/metrics/histogram_unittest.cc b/base/metrics/histogram_unittest.cc
index 41e36faa3c50e7b32db1a8a81899ccb42bc49ff2..df43e65fdef27841af2de2cdeec4bc755c5607cd 100644
--- a/base/metrics/histogram_unittest.cc
+++ b/base/metrics/histogram_unittest.cc
@@ -24,15 +24,13 @@ namespace base {
 
 class HistogramTest : 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();