Update platform classes to use OVERRIDE / FINAL when needed

Source/platform/graphics/DiscardablePixelRef.h

 /*
  * Copyright (C) 2013 Google 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 23 matching lines @@
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 
 namespace WebCore {
 
 // Class for allocating the DiscardablePixelRef object.
 class PLATFORM_EXPORT DiscardablePixelRefAllocator : public SkBitmap::Allocator {
     // SkBitmap::Allocator implementation. The discardable memory allocated
     // after this call is locked and will not be purged until next
     // onUnlockPixels().
-    virtual bool allocPixelRef(SkBitmap*, SkColorTable*);
+    virtual bool allocPixelRef(SkBitmap*, SkColorTable*) OVERRIDE;
 };
 
 // PixelRef object whose memory can be discarded when pixels are unlocked.
 class PLATFORM_EXPORT DiscardablePixelRef : public SkPixelRef {
 public:
     DiscardablePixelRef(const SkImageInfo&, PassOwnPtr<SkMutex>);
     ~DiscardablePixelRef();
 
     static bool isDiscardable(SkPixelRef*);
     bool allocAndLockDiscardableMemory(size_t);
 
     SK_DECLARE_UNFLATTENABLE_OBJECT()
 
 protected:
     // SkPixelRef implementation.
-    virtual void* onLockPixels(SkColorTable**);
-    virtual void onUnlockPixels();
+    virtual void* onLockPixels(SkColorTable**) OVERRIDE;
+    virtual void onUnlockPixels() OVERRIDE;
 
 private:
     void* m_lockedMemory;
     OwnPtr<blink::WebDiscardableMemory> m_discardable;
     OwnPtr<SkMutex> m_mutex;
 };
 
 } // namespace WebCore
 
 #endif