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

Source/core/timing/PerformanceBase.h

Index: Source/core/timing/PerformanceBase.h
diff --git a/Source/core/timing/PerformanceBase.h b/Source/core/timing/PerformanceBase.h
index f2b8f1e74faa7f225296ab675959f967c1eeffe0..344ee39bd06f292308b24db49d8b58f9d2d4ff84 100644
--- a/Source/core/timing/PerformanceBase.h
+++ b/Source/core/timing/PerformanceBase.h
@@ -53,9 +53,9 @@ using PerformanceEntryVector = HeapVector<Member<PerformanceEntry>>;
 class CORE_EXPORT PerformanceBase : public RefCountedGarbageCollectedEventTargetWithInlineData<PerformanceBase> {
     REFCOUNTED_GARBAGE_COLLECTED_EVENT_TARGET(PerformanceBase);
 public:
-    virtual ~PerformanceBase();
+    ~PerformanceBase() override;
 
-    virtual const AtomicString& interfaceName() const override;
+    const AtomicString& interfaceName() const override;
 
     virtual PerformanceTiming* timing() const;
     double now() const;