Implement suspend/resume for IntersectionObserver notifications.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 3941 matching lines @@
     m_viewportIntersection.intersect(viewport);
 }
 
 void FrameView::updateViewportIntersectionsForSubtree(LifeCycleUpdateOption phases)
 {
     bool hadValidIntersection = m_viewportIntersectionValid;
     bool hadEmptyIntersection = m_viewportIntersection.isEmpty();
     updateViewportIntersectionIfNeeded();
 
     // Notify javascript IntersectionObservers
-    if (phases == AllPhases)
-        frame().document()->ensureIntersectionObserverController().computeTrackedIntersectionObservations();
+    if (phases == AllPhases && frame().document()->intersectionObserverController())
+        frame().document()->intersectionObserverController()->computeTrackedIntersectionObservations();
 
     // Adjust render throttling for iframes based on visibility
     bool shouldNotify = !hadValidIntersection || hadEmptyIntersection != m_viewportIntersection.isEmpty();
     if (shouldNotify && !m_renderThrottlingObserverNotificationFactory->isPending())
         m_frame->frameScheduler()->timerTaskRunner()->postTask(BLINK_FROM_HERE, m_renderThrottlingObserverNotificationFactory->cancelAndCreate());
 
     if (!m_needsUpdateViewportIntersectionInSubtree)
         return;
     m_needsUpdateViewportIntersectionInSubtree = false;
 
@@ skipping 50 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink