Update {virtual,override} to follow C++11 style in content.

content/renderer/device_sensors/device_sensor_event_pump.h

Index: content/renderer/device_sensors/device_sensor_event_pump.h
diff --git a/content/renderer/device_sensors/device_sensor_event_pump.h b/content/renderer/device_sensors/device_sensor_event_pump.h
index 43e0f64dca49f79e6df0e170aa6a02a992baa962..45e028d8679223b34ecde43ff1317bf7a7180592 100644
--- a/content/renderer/device_sensors/device_sensor_event_pump.h
+++ b/content/renderer/device_sensors/device_sensor_event_pump.h
@@ -22,7 +22,7 @@ class CONTENT_EXPORT DeviceSensorEventPump
       base::Time::kMicrosecondsPerSecond / kDefaultPumpFrequencyHz;
 
   // PlatformEventObserver
-  virtual void Start(blink::WebPlatformEventListener* listener) override {
+  void Start(blink::WebPlatformEventListener* listener) override {
     DVLOG(2) << "requested start";
 
     if (state_ != STOPPED)
@@ -34,7 +34,7 @@ class CONTENT_EXPORT DeviceSensorEventPump
     state_ = PENDING_START;
   }
 
-  virtual void Stop() override {
+  void Stop() override {
     DVLOG(2) << "stop";
 
     if (state_ == STOPPED)
@@ -55,7 +55,7 @@ class CONTENT_EXPORT DeviceSensorEventPump
         pump_delay_microseconds_(kDefaultPumpDelayMicroseconds),
         state_(STOPPED) {}
 
-  virtual ~DeviceSensorEventPump() {
+  ~DeviceSensorEventPump() override {
     PlatformEventObserver<ListenerType>::StopIfObserving();
   }