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

Source/core/timing/PerformanceMark.h

Index: Source/core/timing/PerformanceMark.h
diff --git a/Source/core/timing/PerformanceMark.h b/Source/core/timing/PerformanceMark.h
index 5cc698671bd9d1b7cd66133fde6051644fae6c8f..7c4dc6457537010af8bb8485c266b063365cb879 100644
--- a/Source/core/timing/PerformanceMark.h
+++ b/Source/core/timing/PerformanceMark.h
@@ -40,7 +40,7 @@ public:
         return new PerformanceMark(name, startTime);
     }
 
-    virtual bool isMark() override { return true; }
+    bool isMark() override { return true; }
 
     DEFINE_INLINE_VIRTUAL_TRACE()
     {
@@ -51,7 +51,7 @@ private:
     PerformanceMark(const String& name, double startTime)
         : PerformanceEntry(name, "mark", startTime, startTime) { }
 
-    virtual ~PerformanceMark() { }
+    ~PerformanceMark() override { }
 };
 
 } // namespace blink