Use intersection observer to control frame throttling

third_party/WebKit/Source/core/dom/ElementVisibilityObserver.cpp

 // 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.
 
 #include "core/dom/ElementVisibilityObserver.h"
 
 #include "core/dom/Element.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "core/frame/LocalFrame.h"
 #include "wtf/Functional.h"
@@ skipping 28 matching lines @@
     m_element.release();
     return;
   }
 
   DCHECK(!m_intersectionObserver);
   m_intersectionObserver = IntersectionObserver::create(
       Vector<Length>(), Vector<float>({std::numeric_limits<float>::min()}),
       &document, WTF::bind(&ElementVisibilityObserver::onVisibilityChanged,
                            wrapWeakPersistent(this)));
   DCHECK(m_intersectionObserver);
+  m_intersectionObserver->setInitialState(
+      IntersectionObserver::InitialState::kAuto);
   m_intersectionObserver->observe(m_element.release());
 }
 
 void ElementVisibilityObserver::stop() {
   // TODO(zqzhang): IntersectionObserver does not work for RemoteFrame,
   // so |m_intersectionObserver| may be null at this point after start().
   // Replace this early return with DCHECK when this has been fixed. See
   // https://crbug.com/615156
   if (!m_intersectionObserver)
     return;
 
   m_intersectionObserver->disconnect();
   m_intersectionObserver = nullptr;
 }
 
+void ElementVisibilityObserver::deliverObservationsForTesting() {
+  m_intersectionObserver->deliver();
+}
+
 DEFINE_TRACE(ElementVisibilityObserver) {
   visitor->trace(m_element);
   visitor->trace(m_intersectionObserver);
 }
 
 void ElementVisibilityObserver::onVisibilityChanged(
     const HeapVector<Member<IntersectionObserverEntry>>& entries) {
   bool isVisible = entries.last()->intersectionRatio() > 0.f;
   (*m_callback.get())(isVisible);
 }
 
 }  // namespace blink