Clean up forward declarations in Source/core

Source/core/plugins/PluginView.h

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2014 Opera Software ASA. 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.
@@ skipping 14 matching lines @@
  */
 
 #ifndef PluginView_h
 #define PluginView_h
 
 #include "platform/Widget.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "wtf/text/WTFString.h"
 #include <v8.h>
 
-struct NPObject;
-
 namespace blink { class WebLayer; }
 
 namespace blink {
 
 class ResourceError;
 class ResourceResponse;
-class Scrollbar;
 
 class PluginView : public Widget {
 public:
     virtual bool isPluginView() const override final { return true; }
 
     virtual blink::WebLayer* platformLayer() const { return 0; }
     virtual v8::Local<v8::Object> scriptableObject(v8::Isolate*) { return v8::Local<v8::Object>(); }
     virtual bool getFormValue(String&) { return false; }
     virtual bool wantsWheelEvents() { return false; }
     virtual bool supportsKeyboardFocus() const { return false; }
@@ skipping 12 matching lines @@
 
 protected:
     PluginView() : Widget() { }
 };
 
 DEFINE_TYPE_CASTS(PluginView, Widget, widget, widget->isPluginView(), widget.isPluginView());
 
 } // namespace blink
 
 #endif // PluginView_h