Cleanup namespace usage in public/platform/{Web[P-W]*,linux/*}.h

public/platform/WebScrollbarLayer.h

 /*
  * Copyright (C) 2012 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
@@ skipping 13 matching lines @@
  */
 
 #ifndef WebScrollbarLayer_h
 #define WebScrollbarLayer_h
 
 #include "WebLayer.h"
 #include "WebScrollbarThemeGeometry.h"
 #include "WebScrollbarThemePainter.h"
 
 namespace blink {
-class Scrollbar;
-}
-
-namespace blink {
 
 class WebScrollbarLayer {
 public:
     virtual ~WebScrollbarLayer() { }
 
     virtual WebLayer* layer() = 0;
 
     virtual void setScrollLayer(WebLayer*) = 0;
     virtual void setClipLayer(WebLayer*) = 0;
 };
 
 } // namespace blink
 
 #endif // WebScrollbarLayer_h