Fix virtual/override/final usage in the rest of Source/core/.

Source/core/timing/Performance.h

Index: Source/core/timing/Performance.h
diff --git a/Source/core/timing/Performance.h b/Source/core/timing/Performance.h
index 33f1b5aa1eba42ebc8fb1081d7e6671c4f37ce15..92c9ca177416a8cdcd2dd5a7b6bb4a18bc2bb9eb 100644
--- a/Source/core/timing/Performance.h
+++ b/Source/core/timing/Performance.h
@@ -49,9 +49,9 @@ public:
     {
         return new Performance(frame);
     }
-    virtual ~Performance();
+    ~Performance() override;
 
-    virtual ExecutionContext* executionContext() const override;
+    ExecutionContext* executionContext() const override;
 
     MemoryInfo* memory();
     PerformanceNavigation* navigation() const;