Clean up forward declarations in Source/platform

Source/platform/scroll/ScrollbarTheme.h

 /*
  * Copyright (C) 2008 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 17 matching lines @@
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/IntRect.h"
 #include "platform/scroll/ScrollTypes.h"
 
 namespace blink {
 
 class GraphicsContext;
 class PlatformMouseEvent;
 class ScrollbarThemeClient;
-class ScrollView;
 
 class PLATFORM_EXPORT ScrollbarTheme {
     WTF_MAKE_NONCOPYABLE(ScrollbarTheme); WTF_MAKE_FAST_ALLOCATED;
 public:
     ScrollbarTheme() { }
     virtual ~ScrollbarTheme() { }
 
     virtual void updateEnabledState(ScrollbarThemeClient*) { }
 
     virtual bool paint(ScrollbarThemeClient*, GraphicsContext*, const IntRect& damageRect);
@@ skipping 84 matching lines @@
     static void setMockScrollbarsEnabled(bool flag);
     static bool mockScrollbarsEnabled();
 
 private:
     static ScrollbarTheme* nativeTheme(); // Must be implemented to return the correct theme subclass.
     static bool gMockScrollbarsEnabled;
 };
 
 }
 #endif