Ignore setting of navigation starting points for detached documents.

third_party/WebKit/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 3704 matching lines @@
     return !focusChangeBlocked;
 }
 
 void Document::clearFocusedElement()
 {
     setFocusedElement(nullptr, FocusParams(SelectionBehaviorOnFocus::None, WebFocusTypeNone, nullptr));
 }
 
 void Document::setSequentialFocusNavigationStartingPoint(Node* node)
 {
+    if (!m_frame)
+        return;
     if (!node) {
         m_sequentialFocusNavigationStartingPoint = nullptr;
         return;
     }
     ASSERT(node->document() == this);
     if (!m_sequentialFocusNavigationStartingPoint)
         m_sequentialFocusNavigationStartingPoint = Range::create(*this);
     m_sequentialFocusNavigationStartingPoint->selectNodeContents(node, ASSERT_NO_EXCEPTION);
 }
 
@@ skipping 2263 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     Document::WeakDocumentSet& set = Document::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