Fix virtual/override/final usage in Source/core/dom/.

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 332 matching lines @@
 }
 #endif
 
 // This class doesn't work with non-Document ExecutionContext.
 class AutofocusTask final : public ExecutionContextTask {
 public:
     static PassOwnPtr<AutofocusTask> create()
     {
         return adoptPtr(new AutofocusTask());
     }
-    virtual ~AutofocusTask() { }
+    ~AutofocusTask() override { }
 
 private:
     AutofocusTask() { }
-    virtual void performTask(ExecutionContext* context) override
+    void performTask(ExecutionContext* context) override
     {
         Document* document = toDocument(context);
         if (RefPtrWillBeRawPtr<Element> element = document->autofocusElement()) {
             document->setAutofocusElement(0);
             element->focus();
         }
     }
 };
 
 DocumentVisibilityObserver::DocumentVisibilityObserver(Document& document)
@@ skipping 5413 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif