Adjust representation of liveDocumentSet() to help diagnose instability.

third_party/WebKit/Source/core/dom/Document.h

 /*
  * 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, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 1051 matching lines @@
     void incrementNodeCount() { m_nodeCount++; }
     void decrementNodeCount()
     {
         DCHECK_GT(m_nodeCount, 0);
         m_nodeCount--;
     }
     int nodeCount() const { return m_nodeCount; }
 
     SnapCoordinator* snapCoordinator();
 
-    using WeakDocumentSet = HeapHashSet<WeakMember<Document>>;
-    static WeakDocumentSet& liveDocumentSet();
-
     WebTaskRunner* loadingTaskRunner() const;
     WebTaskRunner* timerTaskRunner() const;
 
     void enforceStrictMixedContentChecking();
 
     bool mayContainV0Shadow() const { return m_mayContainV0Shadow; }
 
     ShadowCascadeOrder shadowCascadeOrder() const { return m_shadowCascadeOrder; }
     void setShadowCascadeOrder(ShadowCascadeOrder);
 
@@ skipping 369 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h