Refactor frame navigation/detach state cleanup to be more sane.

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 2148 matching lines @@
     // notifyContextDestroyed() for a document that doesn't get detached.
     // If such a document has any observer, the observer won't get
     // a contextDestroyed() notification. This can happen for a document
     // created by DOMImplementation::createDocument().
     DocumentLifecycleNotifier::notifyContextDestroyed();
     ExecutionContext::notifyContextDestroyed();
 }
 
 void Document::prepareForDestruction()
 {
-    m_markers->prepareForDestruction();
-    disconnectDescendantFrames();
+    ASSERT(!m_frame || m_frame->tree().childCount() == 0);
 
-    // The process of disconnecting descendant frames could have already detached us.
     if (!isActive())
         return;
 
+    ScriptForbiddenScope forbidScript;
+    // We detach the FrameView's custom scroll bars as early as
+    // possible to prevent detach() from messing with the view
+    // such that its scroll bars won't be torn down.
+    //
+    // FIXME: We should revisit this.
+    view()->prepareForDetach();
+    m_markers->prepareForDestruction();
     if (LocalDOMWindow* window = this->domWindow())
         window->willDetachDocumentFromFrame();
     detach();
 }
 
 void Document::removeAllEventListeners()
 {
     ContainerNode::removeAllEventListeners();
 
     if (LocalDOMWindow* domWindow = this->domWindow())
@@ skipping 3518 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