Standardize usage of virtual/override/final in media/

media/cast/receiver/audio_decoder.cc

Index: media/cast/receiver/audio_decoder.cc
diff --git a/media/cast/receiver/audio_decoder.cc b/media/cast/receiver/audio_decoder.cc
index 402ff3b012bf4416e81409bf500fae818f90781e..5f4720e8fc5298797bdca3bb978bf8c334ee599d 100644
--- a/media/cast/receiver/audio_decoder.cc
+++ b/media/cast/receiver/audio_decoder.cc
@@ -116,9 +116,9 @@ class AudioDecoder::OpusImpl : public AudioDecoder::ImplBase {
   }
 
  private:
-  virtual ~OpusImpl() {}
+  ~OpusImpl() override {}
 
-  virtual void RecoverBecauseFramesWereDropped() override {
+  void RecoverBecauseFramesWereDropped() override {
     // Passing NULL for the input data notifies the decoder of frame loss.
     const opus_int32 result =
         opus_decode_float(
@@ -126,7 +126,7 @@ class AudioDecoder::OpusImpl : public AudioDecoder::ImplBase {
     DCHECK_GE(result, 0);
   }
 
-  virtual scoped_ptr<AudioBus> Decode(uint8* data, int len) override {
+  scoped_ptr<AudioBus> Decode(uint8* data, int len) override {
     scoped_ptr<AudioBus> audio_bus;
     const opus_int32 num_samples_decoded = opus_decode_float(
         opus_decoder_, data, len, buffer_.get(), max_samples_per_frame_, 0);
@@ -175,9 +175,9 @@ class AudioDecoder::Pcm16Impl : public AudioDecoder::ImplBase {
   }
 
  private:
-  virtual ~Pcm16Impl() {}
+  ~Pcm16Impl() override {}
 
-  virtual scoped_ptr<AudioBus> Decode(uint8* data, int len) override {
+  scoped_ptr<AudioBus> Decode(uint8* data, int len) override {
     scoped_ptr<AudioBus> audio_bus;
     const int num_samples = len / sizeof(int16) / num_channels_;
     if (num_samples <= 0)