Clean up forward declarations in Source/core

Source/core/frame/Frame.h

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999-2001 Lars Knoll <knoll@kde.org>
  *                     1999-2001 Antti Koivisto <koivisto@kde.org>
  *                     2000-2001 Simon Hausmann <hausmann@kde.org>
  *                     2000-2001 Dirk Mueller <mueller@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
@@ skipping 30 matching lines @@
 class FrameHost;
 class FrameOwner;
 class HTMLFrameOwnerElement;
 class DOMWindow;
 class KURL;
 class Page;
 class RenderPart;
 class Settings;
 class WebLayer;
 
-struct Referrer;
-
 class Frame : public RefCountedWillBeGarbageCollectedFinalized<Frame> {
 public:
     virtual ~Frame();
 
     virtual void trace(Visitor*);
 
     virtual bool isLocalFrame() const { return false; }
     virtual bool isRemoteFrame() const { return false; }
 
     virtual DOMWindow* domWindow() const = 0;
@@ skipping 63 matching lines @@
 {
     return m_treeNode;
 }
 
 // Allow equality comparisons of Frames by reference or pointer, interchangeably.
 DEFINE_COMPARISON_OPERATORS_WITH_REFERENCES_REFCOUNTED(Frame)
 
 } // namespace blink
 
 #endif // Frame_h