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

media/audio/agc_audio_stream.h

Index: media/audio/agc_audio_stream.h
diff --git a/media/audio/agc_audio_stream.h b/media/audio/agc_audio_stream.h
index d0ac2bfef36cb37ea72bc465652995e197751a89..a2958ce391a6636a66314506d28bd6bbd5ce0633 100644
--- a/media/audio/agc_audio_stream.h
+++ b/media/audio/agc_audio_stream.h
@@ -138,7 +138,7 @@ class MEDIA_EXPORT AgcAudioStream : public AudioInterface {
   // be read in each AudioInputCallback::OnData() callback and fed to the
   // render-side AGC. User must call StartAgc() as well to start measuring
   // the microphone level.
-  virtual bool SetAutomaticGainControl(bool enabled) override {
+  bool SetAutomaticGainControl(bool enabled) override {
     DVLOG(1) << "SetAutomaticGainControl(enabled=" << enabled << ")";
     DCHECK(thread_checker_.CalledOnValidThread());
     agc_is_enabled_ = enabled;
@@ -146,7 +146,7 @@ class MEDIA_EXPORT AgcAudioStream : public AudioInterface {
   }
 
   // Gets the current automatic gain control state.
-  virtual bool GetAutomaticGainControl() override {
+  bool GetAutomaticGainControl() override {
     DCHECK(thread_checker_.CalledOnValidThread());
     return agc_is_enabled_;
   }