Use intersection observer to control frame throttling

third_party/WebKit/Source/core/dom/ElementVisibilityObserver.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 ElementVisibilityObserver_h
 #define ElementVisibilityObserver_h
 
 #include "core/CoreExport.h"
 #include "core/dom/IntersectionObserver.h"
 #include "platform/heap/Heap.h"
@@ skipping 18 matching lines @@
 
  public:
   using VisibilityCallback = Function<void(bool), WTF::SameThreadAffinity>;
 
   ElementVisibilityObserver(Element*, std::unique_ptr<VisibilityCallback>);
   virtual ~ElementVisibilityObserver();
 
   void start();
   void stop();
 
+  void deliverObservationsForTesting();

[szager1, 2016/10/25 22:39:35]

Can we avoid this by adding calls to runPendingTasks() in the test code?

[Sami, 2016/10/26 17:59:35]

Unfortunately FrameThrottlingTest::ThrottleSubtreeAtomically needs the ability
to trigger specific observers to make sure we're not relying on the order in
which they are delivered.

+
   DECLARE_VIRTUAL_TRACE();
 
  private:
   class ElementVisibilityCallback;
 
   void onVisibilityChanged(
       const HeapVector<Member<IntersectionObserverEntry>>&);
 
   Member<Element> m_element;
   Member<IntersectionObserver> m_intersectionObserver;
   std::unique_ptr<VisibilityCallback> m_callback;
 };
 
 }  // namespace blink
 
 #endif  // ElementVisibilityObserver_h