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

Source/web/PluginPlaceholderImpl.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 PluginPlaceholderImpl_h
 #define PluginPlaceholderImpl_h
 
 #include "core/plugins/PluginPlaceholder.h"
 #include "platform/heap/Handle.h"
 #include "platform/heap/Visitor.h"
@@ skipping 15 matching lines @@
 public:
     static PassOwnPtrWillBeRawPtr<PluginPlaceholderImpl> create(PassOwnPtr<WebPluginPlaceholder> webPluginPlaceholder, Document& document)
     {
         ASSERT(webPluginPlaceholder);
         return adoptPtrWillBeNoop(new PluginPlaceholderImpl(webPluginPlaceholder, document));
     }
 
 #if ENABLE(OILPAN)
     ~PluginPlaceholderImpl();
 #else
-    virtual ~PluginPlaceholderImpl() override;
+    ~PluginPlaceholderImpl() override;
 #endif
 
     DECLARE_VIRTUAL_TRACE();
 
     // PluginPlaceholder methods
-    virtual void loadIntoContainer(ContainerNode&) override;
+    void loadIntoContainer(ContainerNode&) override;
 
     // Visible for testing.
     WebPluginPlaceholder* webPluginPlaceholder() const { return m_webPluginPlaceholder.get(); }
 
 private:
     PluginPlaceholderImpl(PassOwnPtr<WebPluginPlaceholder>, Document&);
 
     // Update the placeholder element with fresh content.
     void update();
 
     OwnPtr<WebPluginPlaceholder> m_webPluginPlaceholder;
     RefPtrWillBeMember<PluginPlaceholderElement> m_placeholderElement;
 };
 
 } // namespace blink
 
 #endif // PluginPlaceholderImpl_h