Fix virtual/override/final usage in Source/platform/.

Source/platform/mediastream/MediaStreamWebAudioSource.h

Index: Source/platform/mediastream/MediaStreamWebAudioSource.h
diff --git a/Source/platform/mediastream/MediaStreamWebAudioSource.h b/Source/platform/mediastream/MediaStreamWebAudioSource.h
index 6da07739ecc8a979113edd860a58d6c9594e7993..4b42ced6782cce04c3c2c86e5b18a295d72f10df 100644
--- a/Source/platform/mediastream/MediaStreamWebAudioSource.h
+++ b/Source/platform/mediastream/MediaStreamWebAudioSource.h
@@ -46,13 +46,13 @@ class MediaStreamWebAudioSource : public AudioSourceProvider {
 public:
     static PassOwnPtr<MediaStreamWebAudioSource> create(PassOwnPtr<WebAudioSourceProvider> provider) { return adoptPtr(new MediaStreamWebAudioSource(provider)); }
 
-    virtual ~MediaStreamWebAudioSource();
+    ~MediaStreamWebAudioSource() override;
 
 private:
     explicit MediaStreamWebAudioSource(PassOwnPtr<WebAudioSourceProvider>);
 
     // blink::AudioSourceProvider implementation.
-    virtual void provideInput(AudioBus*, size_t framesToProcess) override;
+    void provideInput(AudioBus*, size_t framesToProcess) override;
 
     OwnPtr<WebAudioSourceProvider> m_webAudioSourceProvider;
 };