IntersectionObserver: make order of notifications deterministic.

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

 // Copyright 2016 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 IntersectionObserver_h
 #define IntersectionObserver_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "core/dom/IntersectionObservation.h"
 #include "core/dom/IntersectionObserverEntry.h"
@@ skipping 32 matching lines @@
     const Length& rightMargin() const { return m_rightMargin; }
     const Length& bottomMargin() const { return m_bottomMargin; }
     const Length& leftMargin() const { return m_leftMargin; }
     void computeIntersectionObservations();
     void enqueueIntersectionObserverEntry(IntersectionObserverEntry&);
     void applyRootMargin(LayoutRect&) const;
     unsigned firstThresholdGreaterThan(float ratio) const;
     void deliver();
     void removeObservation(IntersectionObservation&);
     bool hasEntries() const { return m_entries.size(); }
-    const HeapHashSet<WeakMember<IntersectionObservation>>& observations() const { return m_observations; }
+    const HeapLinkedHashSet<WeakMember<IntersectionObservation>>& observations() const { return m_observations; }
 
     DECLARE_TRACE();
 
 private:
     explicit IntersectionObserver(IntersectionObserverCallback&, Node&, const Vector<Length>& rootMargin, const Vector<float>& thresholds);
     void clearWeakMembers(Visitor*);
 
     Member<IntersectionObserverCallback> m_callback;
     WeakMember<Node> m_root;
-    HeapHashSet<WeakMember<IntersectionObservation>> m_observations;
+    HeapLinkedHashSet<WeakMember<IntersectionObservation>> m_observations;
     HeapVector<Member<IntersectionObserverEntry>> m_entries;
     Vector<float> m_thresholds;
     Length m_topMargin;
     Length m_rightMargin;
     Length m_bottomMargin;
     Length m_leftMargin;
 };
 
 } // namespace blink
 
 #endif // IntersectionObserver_h