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

Source/core/layout/LayoutTestHelper.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef LayoutTestHelper_h
 #define LayoutTestHelper_h
 
 #include "core/dom/Document.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLElement.h"
 #include "core/testing/DummyPageHolder.h"
 #include "wtf/OwnPtr.h"
 #include <gtest/gtest.h>
 
 namespace blink {
 
 class RenderingTest : public testing::Test {
 protected:
-    virtual void SetUp() override;
+    void SetUp() override;
 
     Document& document() const { return m_pageHolder->document(); }
 
     void setBodyInnerHTML(const String& htmlContent)
     {
         document().body()->setInnerHTML(htmlContent, ASSERT_NO_EXCEPTION);
         document().view()->updateAllLifecyclePhases();
     }
 
     void enableCompositing()
     {
         m_pageHolder->page().settings().setAcceleratedCompositingEnabled(true);
         document().view()->updateAllLifecyclePhases();
     }
 
 private:
     Page::PageClients m_pageClients;
     OwnPtr<DummyPageHolder> m_pageHolder;
 };
 
 } // namespace blink
 
 #endif // LayoutTestHelper_h