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

Source/platform/mediastream/MediaStreamCenter.h

Index: Source/platform/mediastream/MediaStreamCenter.h
diff --git a/Source/platform/mediastream/MediaStreamCenter.h b/Source/platform/mediastream/MediaStreamCenter.h
index a54dca8aee3095e03a7c27f7e364ed6ba5635ca7..d6e9d3b81cbf1fbc6c0d3ed759ea2bb5f438578d 100644
--- a/Source/platform/mediastream/MediaStreamCenter.h
+++ b/Source/platform/mediastream/MediaStreamCenter.h
@@ -50,7 +50,7 @@ class WebMediaStreamTrack;
 class PLATFORM_EXPORT MediaStreamCenter final : public WebMediaStreamCenterClient {
     WTF_MAKE_NONCOPYABLE(MediaStreamCenter);
 public:
-    virtual ~MediaStreamCenter();
+    ~MediaStreamCenter() override;
 
     static MediaStreamCenter& instance();
 
@@ -66,7 +66,7 @@ public:
     void didStopLocalMediaStream(MediaStreamDescriptor*);
 
     // blink::WebMediaStreamCenterClient
-    virtual void stopLocalMediaStream(const WebMediaStream&) override;
+    void stopLocalMediaStream(const WebMediaStream&) override;
 
 private:
     MediaStreamCenter();