IntersectionObserver: second cut.

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

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IntersectionObserverEntry_h
+#define IntersectionObserverEntry_h
+
+#include "bindings/core/v8/ScriptWrappable.h"
+#include "core/dom/ClientRect.h"
+#include "platform/geometry/IntRect.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class Element;
+
+class IntersectionObserverEntry : public GarbageCollectedFinalized<IntersectionObserverEntry>, public ScriptWrappable {
+    DEFINE_WRAPPERTYPEINFO();
+public:
+    IntersectionObserverEntry(double timestamp, const IntRect& boundingClientRect, const IntRect& rootBounds, const IntRect& intersectionRect, Element*);
+    ~IntersectionObserverEntry();
+
+    double time() const { return m_time; }
+    ClientRect* boundingClientRect() const { return m_boundingClientRect; }
+    ClientRect* rootBounds() const { return m_rootBounds; }
+    ClientRect* intersectionRect() const { return m_intersectionRect; }
+    Element* target() const { return m_target.get(); }
+
+    DECLARE_VIRTUAL_TRACE();
+
+private:
+    double m_time;
+    Member<ClientRect> m_boundingClientRect;
+    Member<ClientRect> m_rootBounds;
+    Member<ClientRect> m_intersectionRect;
+    RefPtrWillBeMember<Element> m_target;

[haraken, 2015/12/22 01:13:30]

In non-oilpan, why doesn't this RefPtr create a cycle?

  IntersectionObserver ==(Member)=> IntersectionObserverEntry ==(RefPtr)=>
Element ==(RefPtr)=> Document ==(Persistent)=> IntersectionObserverController
==(Member)=> IntersectionObserver

I guess this should be a RawPtr and cleared when the Element gets destructed.

In oilpan, the cycle is totally fine.

[esprehn, 2015/12/22 07:50:33]

The cycle is fine, it's only until these records are delivered. If JS keeps a
handle to the record it should also keep the element alive. This RefPtr is
correct.

We just need to make sure to either clear or deliver all records. This is the
same as MutationObserver.

[szager1, 2015/12/22 07:53:41]

The IntersectionObserver stops pointing to the IntersectionObserverEntry when
the callback runs.  See IntersectionObserver::deliver().

+};
+
+} // namespace blink
+
+#endif // IntersectionObserverEntry_h