Detach old frame on WebFrame::swap.

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 77 matching lines @@
     HTMLFrameOwnerElement* deprecatedLocalOwner() const;
 
     FrameTree& tree() const;
     ChromeClient& chromeClient() const;
 
     virtual SecurityContext* securityContext() const = 0;
 
     Frame* findFrameForNavigation(const AtomicString& name, Frame& activeFrame);
     Frame* findUnsafeParentScrollPropagationBoundary();
 
+    void prepareSwapFrom(Frame*);
     void finishSwapFrom(Frame*);
 
     bool canNavigate(const Frame&);
     virtual void printNavigationErrorMessage(const Frame&, const char* reason) = 0;
 
     LayoutPart* ownerLayoutObject() const; // LayoutObject for the element that contains this frame.
 
     Settings* settings() const; // can be null
 
     // isLoading() is true when the embedder should think a load is in progress.
@@ skipping 33 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