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

Source/core/testing/NullExecutionContext.cpp

Index: Source/core/testing/NullExecutionContext.cpp
diff --git a/Source/core/testing/NullExecutionContext.cpp b/Source/core/testing/NullExecutionContext.cpp
index c11a1592d3c9a1efaa5b018f2edee6e0918196ac..1f80b2605e3a2fe9ecae48840e0308c1ea1ae812 100644
--- a/Source/core/testing/NullExecutionContext.cpp
+++ b/Source/core/testing/NullExecutionContext.cpp
@@ -16,10 +16,10 @@ namespace {
 class NullEventQueue final : public EventQueue {
 public:
     NullEventQueue() { }
-    virtual ~NullEventQueue() { }
-    virtual bool enqueueEvent(PassRefPtrWillBeRawPtr<Event>) override { return true; }
-    virtual bool cancelEvent(Event*) override { return true; }
-    virtual void close() override { }
+    ~NullEventQueue() override { }
+    bool enqueueEvent(PassRefPtrWillBeRawPtr<Event>) override { return true; }
+    bool cancelEvent(Event*) override { return true; }
+    void close() override { }
 };
 
 } // namespace