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

media/audio/cras/cras_unified_unittest.cc

Index: media/audio/cras/cras_unified_unittest.cc
diff --git a/media/audio/cras/cras_unified_unittest.cc b/media/audio/cras/cras_unified_unittest.cc
index d948f223899bd098d56a8fc3f699758258043871..2f29bfa566419c75328d26c59b486e99b0fd3cc2 100644
--- a/media/audio/cras/cras_unified_unittest.cc
+++ b/media/audio/cras/cras_unified_unittest.cc
@@ -49,7 +49,7 @@ class MockAudioManagerCras : public AudioManagerCras {
   // 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;
   }