Intersection Observer first draft

Source/core/layout/LayoutObject.cpp

Index: Source/core/layout/LayoutObject.cpp
diff --git a/Source/core/layout/LayoutObject.cpp b/Source/core/layout/LayoutObject.cpp
index d08f93804d0716b7c5c97cfe0d2434f2e04f63d9..0036e3c2307df3145735d3cebf63f5d8076e0e3c 100644
--- a/Source/core/layout/LayoutObject.cpp
+++ b/Source/core/layout/LayoutObject.cpp
@@ -2486,6 +2486,10 @@ void LayoutObject::willBeDestroyed()
 
     if (frameView())
         setIsSlowRepaintObject(false);
+
+    if (view() && hasIntersectionObserver()) {

[ojan, 2015/09/21 03:49:09]

Ditto nits about curlies here and below

[MikeB, 2015/09/24 19:04:04]

Done.

+        view()->removeIntersectionObserverTarget(this);
+    }
 }
 
 void LayoutObject::insertedIntoTree()
@@ -2514,6 +2518,10 @@ void LayoutObject::insertedIntoTree()
 
     if (LayoutFlowThread* flowThread = flowThreadContainingBlock())
         flowThread->flowThreadDescendantWasInserted(this);
+
+    if (view() && hasIntersectionObserver()) {
+        view()->addIntersectionObserverTarget(this);
+    }
 }
 
 void LayoutObject::willBeRemovedFromTree()
@@ -2543,6 +2551,10 @@ void LayoutObject::willBeRemovedFromTree()
     // Update cached boundaries in SVG layoutObjects if a child is removed.
     if (parent()->isSVG())
         parent()->setNeedsBoundariesUpdate();
+
+    if (view() && hasIntersectionObserver()) {

[ojan, 2015/09/21 03:49:09]

I'm not sure, but I believe this function gets called from
LayoutObject::willBeDestroyed() via the "remove()" call inside it. So, either
this one or the one in willBeDestroyed isn't needed (I think).

+        view()->removeIntersectionObserverTarget(this);
+    }
 }
 
 void LayoutObject::removeFromLayoutFlowThread()