Intersection Observer first draft

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index 8512bdd52e7dff453044d5204a900f7dbe332ad8..e2ca009b604041c552ee59b72177c85ecebe19dc 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -124,6 +124,7 @@ class HTMLScriptElement;
 class HitTestRequest;
 class IdleRequestCallback;
 class InputDeviceCapabilities;
+class IntersectionObserver;
 class LayoutPoint;
 class LiveNodeListBase;
 class Locale;
@@ -172,6 +173,8 @@ struct IconURL;
 using MouseEventWithHitTestResults = EventWithHitTestResults<PlatformMouseEvent>;
 using ExceptionCode = int;
 
+using IntersectionObservers = WillBeHeapListHashSet<RefPtrWillBeMember<IntersectionObserver>>;
+
 enum StyleResolverUpdateMode {
     // Discards the StyleResolver and rebuilds it.
     FullStyleUpdate,
@@ -677,6 +680,9 @@ public:
     bool hasMutationObservers() const { return m_mutationObserverTypes; }
     void addMutationObserverTypes(MutationObserverOptions types) { m_mutationObserverTypes |= types; }
 
+    void activateIntersectionObserver(IntersectionObserver&);
+    void resumeSuspendedIntersectionObservers();
+
     void updateViewportDescription();
     void processReferrerPolicy(const String& policy);
 
@@ -1060,6 +1066,8 @@ protected:
     void lockCompatibilityMode() { m_compatibilityModeLocked = true; }
     ParserSynchronizationPolicy parserSynchronizationPolicy() const { return m_parserSyncPolicy; }
 
+    void deliverIntersectionObservationsTimerFired(Timer<Document>*);
+
 private:
     friend class IgnoreDestructiveWriteCountIncrementer;
     friend class NthIndexCache;
@@ -1325,6 +1333,10 @@ private:
     Timer<Document> m_loadEventDelayTimer;
     Timer<Document> m_pluginLoadingTimer;
 
+    Timer<Document> m_deliverIntersectionObservationsTimer;
+    IntersectionObservers m_activeIntersectionObservers;
+    IntersectionObservers m_suspendedIntersectionObservers;
+
     ViewportDescription m_viewportDescription;
     ViewportDescription m_legacyViewportDescription;
     Length m_viewportDefaultMinWidth;