Intersection Observer first draft

Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 3475 matching lines @@
     // Turn off style sharing for elements that can gain layers for reasons outside of the style system.
     // See comments in LayoutObject::setStyle().
     // FIXME: Why does gaining a layer from outside the style system require disabling sharing?
     if (isHTMLFrameElementBase(*this) || isHTMLPlugInElement(*this) || isHTMLCanvasElement(*this))
         return false;
     if (Fullscreen::isActiveFullScreenElement(*this))
         return false;
     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)
     if (hasRareData())
         visitor->trace(elementRareData());
     visitor->trace(m_elementData);
 #endif
     ContainerNode::trace(visitor);
 }
 
 } // namespace blink