Intersection Observer first draft

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index ba5c7821706e1435499ee6ffa341c677a4bd57d5..21613093d8be0f93133441cf6e680f631b111d2f 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -3493,6 +3493,28 @@ bool Element::supportsStyleSharing() const
     return true;
 }
 
+void Element::registerIntersectionObserver(IntersectionObserver* observer)
+{
+    size_t index = m_intersectionObservers.find(observer);
+    if (index != WTF::kNotFound)
+        return;
+
+    m_intersectionObservers.append(observer);
+    if (document().layoutView() && layoutObject())
+        document().layoutView()->addIntersectionObserverTarget(layoutObject());
+}
+
+void Element::unregisterIntersectionObserver(IntersectionObserver* observer)
+{
+    size_t index = m_intersectionObservers.find(observer);
+    if (index == WTF::kNotFound)
+        return;
+
+    m_intersectionObservers.remove(index);
+    if (document().layoutView() && layoutObject())
+        document().layoutView()->removeIntersectionObserverTarget(layoutObject());
+}
+
 DEFINE_TRACE(Element)
 {
 #if ENABLE(OILPAN)