Add virtual and OVERRIDE to base/ implementation files

base/system_monitor/system_monitor_unittest.cc

Index: base/system_monitor/system_monitor_unittest.cc
diff --git a/base/system_monitor/system_monitor_unittest.cc b/base/system_monitor/system_monitor_unittest.cc
index eaed974c1107daa6ecde40a16fe4c103e5eca2c9..4f94ce5ef380368df30657d562b25182025df11e 100644
--- a/base/system_monitor/system_monitor_unittest.cc
+++ b/base/system_monitor/system_monitor_unittest.cc
@@ -20,15 +20,15 @@ class PowerTest : public SystemMonitor::PowerObserver {
   }
 
   // PowerObserver callbacks.
-  void OnPowerStateChange(bool on_battery_power) {
+  virtual void OnPowerStateChange(bool on_battery_power) OVERRIDE {
     power_state_changes_++;
   }
 
-  void OnSuspend() {
+  virtual void OnSuspend() OVERRIDE {
     suspends_++;
   }
 
-  void OnResume() {
+  virtual void OnResume() OVERRIDE {
     resumes_++;
   }