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

media/audio/alsa/alsa_output_unittest.cc

Index: media/audio/alsa/alsa_output_unittest.cc
diff --git a/media/audio/alsa/alsa_output_unittest.cc b/media/audio/alsa/alsa_output_unittest.cc
index 2aa19b4c7a933b1dab22766050ccf9a7e7a71d1d..5a7a3aff87f62cb74c80fd6c2eb5129c368bf29f 100644
--- a/media/audio/alsa/alsa_output_unittest.cc
+++ b/media/audio/alsa/alsa_output_unittest.cc
@@ -85,14 +85,14 @@ class MockAudioManagerAlsa : public AudioManagerAlsa {
   // of active output streams. It is because the number of active streams
   // is managed inside MakeAudioOutputStream, and we don't use
   // MakeAudioOutputStream to create the stream in the tests.
-  virtual void ReleaseOutputStream(AudioOutputStream* stream) override {
+  void ReleaseOutputStream(AudioOutputStream* stream) override {
     DCHECK(stream);
     delete stream;
   }
 
   // We don't mock this method since all tests will do the same thing
   // and use the current task runner.
-  virtual scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() override {
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() override {
     return base::MessageLoop::current()->message_loop_proxy();
   }