Update more core classes to use OVERRIDE / FINAL when needed

Source/core/rendering/RenderMultiColumnFlowThread.h

 /*
  * Copyright (C) 2012 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 15 matching lines @@
 
 #ifndef RenderMultiColumnFlowThread_h
 #define RenderMultiColumnFlowThread_h
 
 #include "core/rendering/RenderFlowThread.h"
 
 namespace WebCore {
 
 class RenderMultiColumnFlowThread FINAL : public RenderFlowThread {
 public:
-    ~RenderMultiColumnFlowThread();
+    virtual ~RenderMultiColumnFlowThread();
 
     static RenderMultiColumnFlowThread* createAnonymous(Document*);
 
 private:
     RenderMultiColumnFlowThread();
 
     virtual const char* renderName() const OVERRIDE;
     virtual void computeLogicalHeight(LayoutUnit logicalHeight, LayoutUnit logicalTop, LogicalExtentComputedValues&) const OVERRIDE;
     virtual void autoGenerateRegionsToBlockOffset(LayoutUnit) OVERRIDE;
     virtual LayoutUnit initialLogicalWidth() const OVERRIDE;
     virtual void setPageBreak(LayoutUnit offset, LayoutUnit spaceShortage) OVERRIDE;
     virtual void updateMinimumPageHeight(LayoutUnit offset, LayoutUnit minHeight) OVERRIDE;
 };
 
 } // namespace WebCore
 
 #endif // RenderMultiColumnFlowThread_h