Experiment: assert Document frame detachment.

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 509 matching lines @@
 
 #ifndef NDEBUG
     liveDocumentSet().add(this);
 #endif
 }
 
 Document::~Document()
 {
     ASSERT(!layoutView());
     ASSERT(!parentTreeScope());
+    ASSERT(!m_frame);
 #if !ENABLE(OILPAN)
     ASSERT(m_ranges.isEmpty());
     ASSERT(!hasGuardRefCount());
     // With Oilpan, either the document outlives the visibility observers
     // or the visibility observers and the document die in the same GC round.
     // When they die in the same GC round, the list of visibility observers
     // will not be empty on Document destruction.
     ASSERT(m_visibilityObservers.isEmpty());
 
     if (m_templateDocument)
@@ skipping 5159 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif