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

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 168 matching lines @@
     // Destroy |m_autoSizeInfo| as early as possible, to avoid dereferencing
     // partially destroyed |this| via |m_autoSizeInfo->m_frameView|.
     m_autoSizeInfo.clear();
 
     if (m_postLayoutTasksTimer.isActive())
         m_postLayoutTasksTimer.stop();
 
     if (m_didScrollTimer.isActive())
         m_didScrollTimer.stop();
 
+    // TODO(dcheng): Figure out why the dispose() method is virtual, and why it needs to
+    // call removeFromAXObjectCache() again.
     removeFromAXObjectCache();
 
     // Custom scrollbars should already be destroyed at this point
     ASSERT(!horizontalScrollbar() || !horizontalScrollbar()->isCustomScrollbar());
     ASSERT(!verticalScrollbar() || !verticalScrollbar()->isCustomScrollbar());
 
     setHasHorizontalScrollbar(false); // Remove native scrollbars now before we lose the connection to the HostWindow.
     setHasVerticalScrollbar(false);
 
     ASSERT(!m_scrollCorner);
@@ skipping 3892 matching lines @@
 {
     Settings* settings = frame().settings();
     if (!settings || !settings->rootLayerScrolls())
         return this;
 
     LayoutView* layoutView = this->layoutView();
     return layoutView ? layoutView->scrollableArea() : nullptr;
 }
 
 } // namespace blink