Use Document, rather than document element, for implicit root.

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 118 matching lines @@
 class IntersectionObserverController;
 class LayoutPoint;
 class LiveNodeListBase;
 class Locale;
 class LocalFrame;
 class Location;
 class MainThreadTaskRunner;
 class MediaQueryListListener;
 class MediaQueryMatcher;
 class NodeFilter;
+class NodeIntersectionObserverData;
 class NodeIterator;
 class NthIndexCache;
 class OriginAccessEntry;
 class Page;
 class PlatformMouseEvent;
 class ProcessingInstruction;
 class QualifiedName;
 class Range;
 class LayoutView;
 class ResourceFetcher;
@@ skipping 532 matching lines @@
     bool hasMutationObserversOfType(MutationObserver::MutationType type) const
     {
         return m_mutationObserverTypes & type;
     }
     bool hasMutationObservers() const { return m_mutationObserverTypes; }
     void addMutationObserverTypes(MutationObserverOptions types) { m_mutationObserverTypes |= types; }
 
     WeakPtrWillBeRawPtr<Document> createWeakPtr();
 
     IntersectionObserverController& ensureIntersectionObserverController();
+    NodeIntersectionObserverData& ensureIntersectionObserverData();
 
     void updateViewportDescription();
     void processReferrerPolicy(const String& policy);
 
     // Returns the owning element in the parent document.
     // Returns nullptr if this is the top level document.
     HTMLFrameOwnerElement* ownerElement() const;
 
     // Returns true if this document belongs to a frame that the parent document
     // made invisible (for instance by setting as style display:none).
@@ skipping 696 matching lines @@
 
     ParserSynchronizationPolicy m_parserSyncPolicy;
 
     OriginsUsingFeatures::Value m_originsUsingFeaturesValue;
 
     ClientHintsPreferences m_clientHintsPreferences;
 
     PersistentWillBeMember<CanvasFontCache> m_canvasFontCache;
 
     PersistentWillBeMember<IntersectionObserverController> m_intersectionObserverController;
+    PersistentWillBeMember<NodeIntersectionObserverData> m_intersectionObserverData;
 
     int m_nodeCount;
 };
 
 extern template class CORE_EXTERN_TEMPLATE_EXPORT WillBeHeapSupplement<Document>;
 
 inline bool Document::shouldOverrideLegacyDescription(ViewportDescription::Type origin)
 {
     // The different (legacy) meta tags have different priorities based on the type
     // regardless of which order they appear in the DOM. The priority is given by the
@@ skipping 31 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