Fix virtual/override/final usage in Source/web/.

Source/web/WebHelperPluginImpl.h

Index: Source/web/WebHelperPluginImpl.h
diff --git a/Source/web/WebHelperPluginImpl.h b/Source/web/WebHelperPluginImpl.h
index e2e7e087cdcd63cfeb298f4a235f6022d2349a55..5480d7383a8c9166138f5a55813a88cdd4420f27 100644
--- a/Source/web/WebHelperPluginImpl.h
+++ b/Source/web/WebHelperPluginImpl.h
@@ -53,14 +53,14 @@ class WebHelperPluginImpl final : public WebHelperPlugin {
     WTF_MAKE_FAST_ALLOCATED(WebHelperPluginImpl);
 public:
     // WebHelperPlugin methods:
-    virtual WebPlugin* getPlugin() override;
-    virtual void destroy() override;
+    WebPlugin* getPlugin() override;
+    void destroy() override;
 
 private:
     friend class WebHelperPlugin;
 
     WebHelperPluginImpl();
-    virtual ~WebHelperPluginImpl();
+    ~WebHelperPluginImpl() override;
 
     bool initialize(const String& pluginType, WebLocalFrameImpl*);
     void reallyDestroy(Timer<WebHelperPluginImpl>*);