Add OVERRIDE to base/.

base/metrics/stats_counters.h

Index: base/metrics/stats_counters.h
diff --git a/base/metrics/stats_counters.h b/base/metrics/stats_counters.h
index 9ba35175c7cdc46ac1bddb5a0493a42a271942be..08c29c3309b3c5903051986c7c67b60c86c2837f 100644
--- a/base/metrics/stats_counters.h
+++ b/base/metrics/stats_counters.h
@@ -9,6 +9,7 @@
 #include <string>
 
 #include "base/base_export.h"
+#include "base/compiler_specific.h"
 #include "base/metrics/stats_table.h"
 #include "base/time.h"
 
@@ -164,7 +165,7 @@ class BASE_EXPORT StatsRate : public StatsCounterTimer {
   explicit StatsRate(const std::string& name);
   virtual ~StatsRate();
 
-  virtual void Add(int value);
+  virtual void Add(int value) OVERRIDE;
 
  private:
   StatsCounter counter_;