IntersectionObserver: use nullptr for implicit root.

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

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index 67ac81e35d1c0d983528e25d022c17404db8ee3e..ec60dd67b3d48d645c8d53067b4f4d1909fdebc6 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -136,7 +136,6 @@ class Location;
 class MediaQueryListListener;
 class MediaQueryMatcher;
 class NodeFilter;
-class NodeIntersectionObserverData;
 class NodeIterator;
 class NthIndexCache;
 class OriginAccessEntry;
@@ -813,7 +812,6 @@ class CORE_EXPORT Document : public ContainerNode,
 
   IntersectionObserverController* intersectionObserverController();
   IntersectionObserverController& ensureIntersectionObserverController();
-  NodeIntersectionObserverData& ensureIntersectionObserverData();
 
   ResizeObserverController* resizeObserverController() const {
     return m_resizeObserverController;
@@ -1654,7 +1652,6 @@ class CORE_EXPORT Document : public ContainerNode,
   Member<CanvasFontCache> m_canvasFontCache;
 
   Member<IntersectionObserverController> m_intersectionObserverController;
-  Member<NodeIntersectionObserverData> m_intersectionObserverData;
   Member<ResizeObserverController> m_resizeObserverController;
 
   int m_nodeCount;