Clear the owner element's widget in Document::shutdown().

third_party/WebKit/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 333 matching lines @@
   // Destroy |m_autoSizeInfo| as early as possible, to avoid dereferencing
   // partially destroyed |this| via |m_autoSizeInfo->m_frameView|.
   m_autoSizeInfo.clear();
 
   m_postLayoutTasksTimer.stop();
   m_didScrollTimer.stop();
 
   // FIXME: Do we need to do something here for OOPI?
   HTMLFrameOwnerElement* ownerElement = m_frame->deprecatedLocalOwner();
   // TODO(dcheng): It seems buggy that we can have an owner element that
-  // points to another Widget.
-  if (ownerElement && ownerElement->ownedWidget() == this)
+  // points to another Widget. See https://crbug.com/673170 for an example.

[esprehn, 2016/12/13 23:46:22]

Can we add a commented out DCHECK here with the widget condition you removed?
That way folks know what the comment is about. Also add the description you had
in the review for how we get there here.

[Mariusz Mlynski, 2016/12/14 00:18:03]

Done. The comment would logically better belong inside the if clause, but I
think it's more readable like this. Let me know if you prefer otherwise.

+  if (ownerElement)
     ownerElement->setWidget(nullptr);
 
 #if ENABLE(ASSERT)
   m_hasBeenDisposed = true;
 #endif
 }
 
 void FrameView::detachScrollbars() {
   // Previously, we detached custom scrollbars as early as possible to prevent
   // Document::detachLayoutTree() from messing with the view such that its
@@ skipping 4303 matching lines @@
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.width();
 }
 
 int FrameView::initialViewportHeight() const {
   DCHECK(m_frame->isMainFrame());
   return m_initialViewportSize.height();
 }
 
 }  // namespace blink