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

components/metrics/histogram_manager.h

Index: components/metrics/histogram_manager.h
diff --git a/components/metrics/histogram_manager.h b/components/metrics/histogram_manager.h
index a1f988ace6627c044d3fe5fdfc6462524834aab5..7334ae35f29a0305efdb6fc5d85b3288fdbd73fa 100644
--- a/components/metrics/histogram_manager.h
+++ b/components/metrics/histogram_manager.h
@@ -27,7 +27,7 @@ namespace metrics {
 class HistogramManager : public base::HistogramFlattener {
  public:
   HistogramManager();
-  ~HistogramManager();
+  ~HistogramManager() override;
 
   // Snapshot all histograms to record the delta into |uma_proto_| and then
   // returns the serialized protobuf representation of the record in |data|.