Fix stale focusedElement in unloaded document.

third_party/WebKit/Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc.
  * All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
@@ skipping 2626 matching lines @@
 void Element::focus(const FocusParams& params) {
   if (!isConnected())
     return;
 
   if (document().focusedElement() == this)
     return;
 
   if (!document().isActive())
     return;
 
+  if (isFrameOwnerElement() &&
+      toHTMLFrameOwnerElement(this)->contentDocument()->unloadStarted())

[tkent, 2017/02/17 07:34:00]

contnetDocument() might return nullptr.

+    return;
+
   document().updateStyleAndLayoutIgnorePendingStylesheetsForNode(this);
   if (!isFocusable())
     return;
 
   if (authorShadowRoot() && authorShadowRoot()->delegatesFocus()) {
     if (isShadowIncludingInclusiveAncestorOf(document().focusedElement()))
       return;
 
     // Slide the focus to its inner node.
     Element* found =
@@ skipping 1477 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(Element) {
   if (hasRareData()) {
     visitor->traceWrappers(elementRareData());
   }
   ContainerNode::traceWrappers(visitor);
 }
 
 }  // namespace blink