Use intersection observer to control frame throttling

third_party/WebKit/Source/core/dom/IntersectionObserverController.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 IntersectionObserverController_h
 #define IntersectionObserverController_h
 
 #include "core/dom/ActiveDOMObject.h"
 #include "core/dom/IdleRequestCallback.h"
 #include "core/dom/IntersectionObserver.h"
 #include "platform/heap/Handle.h"
 #include "wtf/HashSet.h"
 
 // Design doc for IntersectionObserver implementation:
 //   https://docs.google.com/a/google.com/document/d/1hLK0eyT5_BzyNS4OkjsnoqqFQDYCbKfyBinj94OnLiQ
 
 namespace blink {
 
+class CancellableTaskFactory;
 class Document;
 
 class IntersectionObserverController : public IdleRequestCallback, public ActiveDOMObject {
     USING_GARBAGE_COLLECTED_MIXIN(IntersectionObserverController);
 public:
     static IntersectionObserverController* create(Document*);
     ~IntersectionObserverController();
 
     void resume() override;
     void handleEvent(IdleDeadline*) override;
 
     void scheduleIntersectionObserverForDelivery(IntersectionObserver&);
     void deliverIntersectionObservations();
     void computeTrackedIntersectionObservations();
     void addTrackedObserver(IntersectionObserver&);
     void removeTrackedObserversForRoot(const Node&);
 
     DECLARE_TRACE();
 
 private:
     explicit IntersectionObserverController(Document*);
 
 private:
+    void deliverLowLatencyNotifications();
+
     // IntersectionObservers for which this is the tracking document.
     HeapHashSet<WeakMember<IntersectionObserver>> m_trackedIntersectionObservers;
     // IntersectionObservers for which this is the execution context of the callback.
     HeapHashSet<Member<IntersectionObserver>> m_pendingIntersectionObservers;
+    HeapHashSet<Member<IntersectionObserver>> m_pendingLowLatencyIntersectionObservers;
+
+    std::unique_ptr<CancellableTaskFactory> m_lowLatencyNotificationTask;
 
     int m_callbackID;
     bool m_callbackFiredWhileSuspended;
+    bool m_lowLatencyCallbackFiredWhileSuspended;
 };
 
 } // namespace blink
 
 #endif // IntersectionObserverController_h