Update remaining core classes to use OVERRIDE / FINAL when needed

Source/core/timing/PerformanceTiming.h

Index: Source/core/timing/PerformanceTiming.h
diff --git a/Source/core/timing/PerformanceTiming.h b/Source/core/timing/PerformanceTiming.h
index cd8ffae7cef4eb62138bbda02bec91bbafb15f58..640b47ef351e99c483e3380e09b693327278522f 100644
--- a/Source/core/timing/PerformanceTiming.h
+++ b/Source/core/timing/PerformanceTiming.h
@@ -44,7 +44,7 @@ struct DocumentTiming;
 class Frame;
 class ResourceLoadTiming;
 
-class PerformanceTiming : public RefCounted<PerformanceTiming>, public ScriptWrappable, public DOMWindowProperty {
+class PerformanceTiming FINAL : public RefCounted<PerformanceTiming>, public ScriptWrappable, public DOMWindowProperty {
 public:
     static PassRefPtr<PerformanceTiming> create(Frame* frame) { return adoptRef(new PerformanceTiming(frame)); }