On Document disposal, only dispose of script runner.

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 557 matching lines @@
     m_docType = nullptr;
     m_focusedElement = nullptr;
     m_hoverNode = nullptr;
     m_activeHoverElement = nullptr;
     m_titleElement = nullptr;
     m_documentElement = nullptr;
     m_contextFeatures = ContextFeatures::defaultSwitch();
     m_userActionElements.documentDidRemoveLastRef();
     m_associatedFormControls.clear();
 
-    m_scriptRunner.clear();
+    m_scriptRunner->dispose();
     detachParser();
 
     m_registrationContext.clear();
 
     // removeDetachedChildren() doesn't always unregister IDs,
     // so tear down scope information upfront to avoid having stale references in the map.
     destroyTreeScopeData();
 
     removeDetachedChildren();
 
@@ skipping 5165 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