Detach all subframes before swapping a frame.

Source/core/frame/Frame.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Simon Hausmann <hausmann@kde.org>
  *                     2000 Stefan Schimanski <1Stein@gmx.de>
  *                     2001 George Staikos <staikos@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov <ap@nypop.com>
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
@@ skipping 75 matching lines @@
 
     // FIXME: We should not be doing all this work inside the destructor
 
 #ifndef NDEBUG
     frameCounter.decrement();
 #endif
 }
 
 void Frame::detachChildren()
 {
+    ASSERT(refCount() > 1);

[kenrb, 2014/09/05 19:28:09]

I'm fine with this, but it should have a comment on it so if somebody has a
reason to remove it later, they at least can be made to think about what they
are doing.

[nasko, 2014/09/05 23:37:29]

Done.

     typedef Vector<RefPtr<Frame> > FrameVector;
     FrameVector childrenToDetach;
     childrenToDetach.reserveCapacity(tree().childCount());
     for (Frame* child = tree().firstChild(); child; child = child->tree().nextSibling())
         childrenToDetach.append(child);
     FrameVector::iterator end = childrenToDetach.end();
     for (FrameVector::iterator it = childrenToDetach.begin(); it != end; ++it)
         (*it)->detach();
 }
 
@@ skipping 93 matching lines @@
     }
     m_owner = 0;
 }
 
 HTMLFrameOwnerElement* Frame::deprecatedLocalOwner() const
 {
     return m_owner && m_owner->isLocal() ? toHTMLFrameOwnerElement(m_owner) : 0;
 }
 
 } // namespace blink